Estimating Shock Success by Monitoring Changes in Spectral Data

ABSTRACT

This document presents a system for managing treatment for an emergency cardiac event. The system includes memory, one or more electronic ports for receiving ECG signals, and a treatment module executable on one or more processing devices. The module is configured to perform a number of transformation on portions of an ECG signal into frequency domain data, obtain one or more previous values derived from one or more time segments of the ECG, and determine, based on the frequency domain data a first value and a second value, determine a probability of therapeutic success. The module is further configured to cause one or more output devices to present an indication of the probability of therapeutic success.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of priority to U.S. ProvisionalApplication Ser. No. 62/249,123, filed on Oct. 30, 2015, the entirecontents of which is hereby incorporated by reference.

TECHNICAL FIELD

This document relates to cardiac resuscitation systems and techniques.

BACKGROUND

Heart attacks are a common cause of death. A heart attack occurs when aportion of the heart tissue loses circulation and, as a result, becomesdamaged (e.g., because of blockage in the heart vasculature). Heartattacks and other abnormalities can lead to ventricular fibrillation(VF), which is an abnormal heart rhythm (arrhythmia) that causes theheart to lose pumping capacity. If such a problem is not correctedquickly—typically within minutes—the rest of the body loses oxygen andthe person dies. Therefore, prompt care of a person undergoingventricular fibrillation can be key to a positive outcome for such aperson.

One common way to treat ventricular fibrillation is through the use ofan electrical defibrillator that delivers a relatively high voltageshock to the heart in order to restore a healthy and regular, rhythmassociated with strong myocardial contractility. People who have hadprevious problems with ventricular fibrillation can be implanted with anautomatic defibrillator that constantly monitors the condition of theirheart and applies a shock when necessary. Other such people can beprovided with a wearable defibrillator in the form of a vest such as theLIFEVEST product from ZOLL Medical Corporation. Other people can betreated using an external defibrillator, such as in a hospital or via anautomatic external defibrillator (AED) of the kind that is frequentlyseen in airports, public gymnasiums, and other public spaces.Defibrillation can be delivered in coordination with cardiopulmonaryresuscitation, which centers on the provision of repeated compressionsto a victim's chest. For example, a rescuer can press downwardrepeatedly with the palms of the hands, or via a mechanical compressiondevice such as the AUTOPULSE non-invasive cardiac support pump from ZOLLMedical Corporation.

People undergoing ventricular fibrillation can be more receptive to adefibrillating shock in some instances compared to others. For example,research has determined that an indication of whether a shock that isdelivered would likely result in successful defibrillation can beobtained using a computation of amplitude spectrum area (AMSA), or othercomputational methods that use either time-based or spectrum-basedanalytic methods to calculate, from an electrocardiogram (ECG), aprediction of defibrillation shock success.

SUMMARY

This document describes systems and techniques that can be used to helpdetermine when an electric shock delivered to a person suffering from VFcan likely be successful, i.e., restore healthy cardiac rhythm. Suchsystems and techniques can also be used to estimate how long a personhas been suffering from cardiac arrest or fibrillation, and use the timeestimate to select the appropriate treatment (e.g., defibrillatingshock, CPR). Systems and methods described herein provide for a spectralanalysis that can result in a recommendation for a patient to be treatedwith an electric shock earlier than would otherwise be the case. Forexample, values output from a spectral analysis (e.g., AMSA, frequencytransform) can be used in determining the appropriate treatment therapyfor a patient at any given time, however, trends in values output fromthe spectral analysis can also be used as an additional factor in makingthe treatment determination. By using this additional information (e.g.,considering changes in the spectral analysis in addition to absolutevalues output from the analysis) in calculating the probability of shocksuccess, suitable therapeutic intervention(s) (e.g., electric shock inplace of CPR) can be administered sooner than later. Techniques formaking such predictions more accurately are also described herein.

Such determinations can be used to guide a person (e.g., a physician,EMT, or lay rescuer) who is performing rescue operations on the personsuffering of VF (also referred to here as a patient or victim). Theguidance can be provided by a portable defibrillator providing anaudio-video indication, such as on a graphical display of thedefibrillator or another device. The guidance can include arecommendation that a shock should or should not be provided, or thatchest compressions of a particular type should be given instead of ashock. Also, a device can display an estimated time since thefibrillations began so as to provide further information to a rescuer.In implementations described below, for example, such systems andtechniques can take into account the success or lack of success in priorattempts to defibrillate the person (e.g., where there has beenrecurrent or refractory VF—where recurrent VF results after a successfulprior defibrillating shock and refractory VF results after anunsuccessful prior defibrillating shock), among other factors, such as acurrent AMSA value for the person and trans-thoracic impedance level ofthe person.

Such systems can also take into account a current AMSA value, an AMSAvalue over a different period of time, a trend in AMSA value over time,a change of AMSA value, a change rate of AMSA value and/or a myocardialviability indicator for recommending chest compressions or deliveranceof a defibrillation shock. AMSA is a value calculated by taking a FastFourier Transform (FFT) of the VF waveform. While FFTs are generallypremised on an assumption of an infinitely long time series, relativelyshort time series (e.g., less than 4 seconds and more preferably closeto 1 second) can be better for predicting a likelihood ofdefibrillation. Short windows are generally improper for the operationof an FFT. As described below, a tapered window, such as a Tukey window,can be used to lessen edge effects from the windowing of ECG data thatis collected for performing the AMSA calculation, which can permit therelative benefits of using a smaller window while lessening thedis-benefits of using the smaller window.

As one example of using AMSA values to make a determination of thelikelihood that a currently-delivered shock with result in successfuldefibrillation, a threshold AMSA value can be set, at which level theshocking ability of a defibrillator is made available to a rescuer, orat which a likelihood of success that is displayed to the rescuer canchange (e.g., AMSA values between X and Y can show a likelihood of mpercent, while AMSA values between Y and Z can show a likelihood valueof n percent) based on whether prior successful defibrillating shocksthat have been given to a patient have been successful. For example, therelevant AMSA threshold for generating a particular output or action ofa defibrillator (such as the display to the user just mentioned) can beadjusted based on determinations about the success of prior shocks andon the trans-thoracic impedance.

Thus, for example, an AMSA value or values can be computed from incomingECG signals from the person, and decisions can be made by comparing thecomputed AMSA value to stored thresholds, where the thresholds canchange based on the other factors, or the AMSA value can be adjustedusing the other factors and then be compared to thresholds that do notchange. Generally, there is no practical difference between changing thevalue and making static the thresholds against which it is comparedversus changing the thresholds and leaving the value set.

Such adjustments, when based on determinations about the success or lackof success of prior defibrillation efforts, can be made in a variety ofways. For example, AMSA threshold values (which are reduced forrecurrent VF) associated with future successful defibrillation have beendetermined to decrease substantially when there has been a priorsuccessful defibrillation during an emergency with a particular patient.(Unless indicated otherwise, all values that are collected, computed,and compared here are for a single adverse cardiac event for a patient.)

Such correlations can be determined by analysis of historicaldefibrillation activity (e.g., collected by portable defibrillatorsdeployed in the field for actual cardiac events), and can be used toproduce a mapping between observed past likelihood of success forvarious AMSA values and levels of prior successful defibrillations. Suchdata can be used, for example, to generate a look-up table or similarstructure that can be loaded on other deployed (e.g., via network and/orwireless data updates) or to-be-deployed defibrillators, which can beconsulted in the future during other cardiac events. For example, thenumber of prior successful defibrillations for an event can be along oneaxis of a table, and an AMSA score can be along another, and those otherdefibrillators can employ both values for a victim, with the tableproducing an indication of a likelihood of a to-be-applied shock beingsuccessful. The table or other data structure can also have additionaldimensions, such as a dimension that identifies trans-thoracicimpedance, and dimensions that identify other variables whose valuesthat have been determined to be relevant to whether an applied shock canlikely be successful.

As noted, a tapering function can be applied to the ECG data, so as toimprove the accuracy of the FFT applied to the data, by preventing thedata from jumping immediately from a zero value up the measured values,and then back down immediately to a zero value at the end of a measuredwindow. Various parameters for the tapering function can also beapplied, such as coefficients to define the slops of the starting andending edges of the function. The particular type of tapering functionused and the coefficients applied to it can be determined by analysis ofECG data and shock outcomes from prior rescue efforts that have beensensed and stored by on-site monitors (e.g., as part of portabledefibrillators), and analyzed after-the-fact as a group to identifycorrelations between particular AMSA values, window sizes, windowshapes, and defibrillation outcomes.

In some implementations, multiple different tapering functions can beapplied to the same data essentially simultaneously, and the resultingAMSA value from one of the functions can be selected, or an AMSA valuecan be generated that is a composite from multiple different taperingfunctions. The window function that is used, the length of the window,and the coefficients for the window can also be adjusted dynamically, sothat one or more of them change during a particular incident, ordeployment, with a particular patient. For example, it can be determinedfrom analysis of prior data that a particular window shape, size, and/orcoefficients are better earlier in an episode of VF than later, so thata defibrillator can be programmed to change such parameters over thecourse of an event. Such changes can be tied to an initial determinationabout how long the patient has been in VF, which can be a function ofuser input (e.g., when the emergency call was made) and parametersmeasured by the defibrillator. Also, changes to the window type, size,and coefficients can be made from readings dynamically made from thepatient under treatment. For example, AMSA values in a particular rangecan be measured better by a particular window type, size, or range ofcoefficients, so that an AMSA measurement made at time n that shows sucha value, can be measured using the other parameters known to work bestwith that AMSA value at time n+1. Other techniques for dynamicallyadjusting the window type, window size, and/or coefficients can also beemployed. The shape of the window can be asymmetric. For instance, theedge of the window that is “older” in time can have a window shape thatresults in a greater level of attenuation that the “newer” portion ofthe windowed data.

Upon a defibrillator making a determination of a likelihood of futuresuccess for defibrillating a patient, the defibrillator can provide anindication to a rescuer about such a determination. For example, thedefibrillator can only allow a shock to be performed when the indicationis sufficiently positive (e.g., over a set percentage of likelihood ofsuccess)—and can only provide a “ready for shock” light or otherindication in such a situation. Also, a defibrillator can provide adisplay—such as a graphic that shows whether defibrillation can likelysucceed (e.g., above a predetermined threshold level of likelihood ofsuccess) or provide a number (e.g., a percentage of likelihood ofsuccess) or other indication (e.g., a grade of A, B, C, D, or F) so thatthe rescuer can determine whether to apply a shock. In some situations,the AMSA value can serve merely to provide a recommendation to the user,with the user able to apply a shock at any time; in other situations(e.g., especially for AEDs to be used by lay rescuers), the AMSA valuecan be used to disable or enable the ability to deliver a shock.

The device (e.g., defibrillator) can also change the indication itpresents in different situations, e.g., a dual-mode defibrillator couldsimply indicate whether defibrillation is advised (and can refuse topermit delivery of a shock when it is not advised) when thedefibrillator is in AED mode, and can provide more nuanced informationwhen the defibrillator is in manual mode, and thus is presumably beingoperated by someone who can better interpret such nuanced informationand act properly on it.

With respect to indications of where a victim is in the process of a VFepisode—e.g., how many minutes since the victim's episode has started—anaverage AMSA value can be determined over a time period so as toidentify more generalized changes in the victim's AMSA values, ratherthan AMSA at a particular point in time or small slice of time. Forexample, AMSA values can be computed for particular points in time orparticular windows in time and those values can be saved (e.g., inmemory of a patient monitor or defibrillator). After multiple suchmeasurements and computations have been made, an average can be computedacross multiple such values. Because AMSA generally decreases (onaverage) over time in an episode, if the average for a particular numberof readings (e.g., a moving average) decreases below a particular valueor decreases below the value over a minimum time period (so as toindicate the general AMSA condition of the victim rather than just atransient reading), the device can provide additional feedback to arescuer.

These general phases of cardiac arrest or VF can be identified, in onerepresentation, as three separate phases (though there can be someoverlap at the edges of the phases): electrical, circulatory, andmetabolic. The electrical phase is the first several minutes of anevent, and marks a period during which electric shock can beparticularly effective in defibrillating the victim's heart andreturning the victim to a relative satisfactory condition. Thecirculatory phase appears to mark a decrease in effectiveness forelectric shock in defibrillating the victim, and particularly in theabsence of chest compressions performed on the victim. As a result, adevice such as a portable defibrillator can be programmed to stopadvising shocks during such a phase (or can advise a shock only whenother determinations indicate that a shock would be particularly likelyto be effective) and can instead advise forceful CPR chest compressions.Such forceful compressions can maximize blood flow through the hearttissue and other parts of the body so as to extend the time that thevictim can survive without lasting or substantial damage.

In the metabolic phase, chest compressions can be relatively ineffectiveas compared to the circulatory phase. For example, where tissue hasbecome ischemic, such as in circulatory phase, the tissue can reactfavorably to the circulation of blood containing some oxygen, but wheretissue has become severely ischemic, such as in metabolic phase, theintroduction of too much oxygen can be harmful to the tissue. As aresult, more gentle compressions for the first period, such as 32seconds, can be advised in the metabolic phase before the rescuer (or amechanical chest compressor controlled to provide appropriate levels ofcompression following the points addressed here) uses a full force.

Other treatments that can be useful in the metabolic phase includeextracorporeal circulation and cooling, either alone, in combinationwith each other, or in combination with other pharmacologicaltreatments. In any event, observation of elapsed time since an event hasbegun and/or observation of the phase in which a victim is in, can beused to control a device or instruct a rescuer to switch from a firstmode of providing care to a second mode of providing care in which theparameters of the provided care differ (e.g., speed or depth of chestcompressions can change, temperature-based therapy can be provided orstopped, or pharmaceuticals can be administered).

In some implementations, such systems and techniques can provide one ormore advantages. For example, determinations of whether a shock shouldbe provided or what advice to provide a rescuer based on the phase avictim is in can be made from values that are already being measured fora patient (e.g., trans-thoracic impedance can already be used by adefibrillator to affect the shape of the voltage of the waveform that isprovided to the patient). For example, determinations about shocks canbe improved compared to simply measuring AMSA, and can thus result inbetter performance for a system and better outcomes for a patient. Inparticular, a defibrillator can cause a rescuer to wait to provide adefibrillating shock until a time at which the shock is more likely tobe effective. As a result, the patient can avoid receiving anineffective shock, and then having to wait another cycle for anothershock (which can end up being equally ineffective). And a system canguide the rescuer in providing a shock, versus providing deep chestcompressions, versus providing progressive chest compressions (or cancause a device to provide such actions automatically), throughout thecourse of a cardiac event. Such a process may, therefore, result in thepatient returning to normal cardiac function more quickly and with lessstress on his or her cardiac system, which can generally lead to betterpatient outcomes.

The use of particular type, duration, and coefficients for making AMSAreadings can result in more accurate instructions being given to a humanor mechanical rescuer, or in enabling or disabling functionality of amedical device. In particular, the feedback provided can result indeterminations about whether to shock or not shock, or to provide chestcompressions, can be more closely aligned with a likelihood of apositive outcome (e.g., defibrillation) for a particular patient, andcan be customized to the present situation of the patient (e.g., asindicated by AMSA readings for the patient).

In one implementation, a system for managing treatment for an emergencycardiac event, includes memory and one or more electronic ports forreceiving signals from sensors for obtaining indications of anelectrocardiogram (ECG) for a patient. The system also includes apatient treatment module executable on one or more processing devices,wherein the patient treatment module is configured to generate transformvalues for a time segment of ECG. The transform values representmagnitudes of two or more frequency components of the ECG. The patienttreatment module is also configured to obtain one or more previousvalues derived from one or more earlier time segments of the ECG,determine, based on the generated transform values, and the one or moreprevious values, at least one of: a) a future therapeutic action fortreating the emergency cardiac event, or b) a phase of the cardiacevent. The patient treatment module is further configured to cause oneor more output devices to present an indication of at least one of thetherapeutic action or the phase of the cardiac event.

In another aspect, a system for treating a patient in cardiac arrestincludes memory, and one or more electronic ports for receiving signalsfrom sensors for obtaining indications of an electrocardiogram (ECG) forthe patient. The system also includes a patient treatment moduleexecutable on one or more processing devices. The patient treatmentmodule is configured to generate transform values that representmagnitudes of two or more frequency components of the ECG, generate atime series from a plurality of the transform values, and determine,based on the time series, a future therapeutic action for treating thecardiac arrest.

In another aspect, a system for managing treatment for an emergencycardiac event includes memory, and one or more electronic ports forreceiving signals from sensors for obtaining indications of anelectrocardiogram (ECG) for a patient. The system also includes apatient treatment module executable on one or more processing devices.The patient treatment module is configured to generate transform valuesfor a time segment of ECG, wherein the transform values representmagnitudes of two or more frequency components of the ECG. The patienttreatment module is also configured to obtain one or more previoustransform values derived from one or more earlier time segments of theECG, determine, based on the generated transform values, and the one ormore previous transform values, an indication of a likelihood of successfrom delivering a defibrillating shock, and cause one or more outputdevices to present the indication of a likelihood of success fromdelivering a defibrillating shock.

In another aspect, this document features one or more machine-readablestorage devices having encoded thereon machine readable instructions forcausing one or more processors to perform various operations. Theoperations include receiving, signals indicative of an electrocardiogram(ECG) of a patient, and generating transform values for a time segmentof the ECG, wherein the transform values represent magnitudes of two ormore frequency components of the ECG. The operations also includeobtaining one or more previous values derived from one or more earliertime segments of the ECG, determining, based on the generated transformvalues, and the one or more previous values, a future therapeutic actionfor treating an emergency cardiac event in the patient, and causing oneor more output devices to present an indication of at least one of thetherapeutic action or the phase of the cardiac event.

In another aspect, this document features one or more machine-readablestorage devices having encoded thereon machine readable instructions forcausing one or more processors to perform various operations thatinclude receiving signals indicative of an electrocardiogram (ECG) of apatient, and generating transform values. The transform values representmagnitudes of two or more frequency components of the ECG. Theoperations also include generating a time series from a plurality of thetransform values, and determining, based on the time series, a futuretherapeutic action for treating a cardiac arrest of the patient.

In another aspect, this document features one or more machine-readablestorage devices having encoded thereon machine readable instructions forcausing one or more processors to perform various operations thatinclude receiving, signals indicative of an electrocardiogram (ECG) of apatient, and generating transform values. The transform values representmagnitudes of two or more frequency components of the ECG. Theoperations also include obtaining one or more previous transform valuesderived from one or more earlier time segments of the ECG, determiningbased on the generated transform values, and the one or more previoustransform values, an indication of a likelihood of success fromdelivering a defibrillating shock, and causing one or more outputdevices to present the indication of a likelihood of success fromdelivering a defibrillating shock.

Implementations of the above aspect can include one or more of thefollowing features.

The patient treatment module can include an ECG analyzer for generatingan amplitude spectrum area (AMSA) value using the transform values. Theprevious values can be derived from one or earlier time segments of theECG are AMSA values. The transform values can be updated at a rate of0.1-10 Hz. The length of the time segment can be in the range betweenabout 1 and 4 seconds. The one or more processing devices can generatethe transform values for the time segment of ECG using a tapered window.The tapered window can be one of: a Tukey window, a Hann window, aBlackman-Harris window, or a Flat Top window. The future therapeuticaction can be determined based at least in part on comparing a valueobtained from the generated transform values to a threshold. Thetransform can include at least one of: Fourier, fast Fourier, discreteFourier, Hilbert, discrete Hilbert, wavelet, and discrete waveletmethods. The therapeutic action can include computing an average basedon the one or more previous values. The average can be also based on avalue obtained from the generated transform values. The one or moreprevious values can be generated via processing of multiple earlier timesegments of the ECG. The processing can be performed two or more timesduring the cardiac event. The one or more output devices can present anaudible or visual feedback of at least one of the indication of thetherapeutic action or the phase of the cardiac event. The therapeuticaction can include delivering a defibrillating shock to the patient. Thetherapeutic action can include initiating or continuing cardiopulmonaryresuscitation (CPR). The therapeutic action can include adjusting acardiopulmonary resuscitation (CPR) technique. The phase can be one of:an electrical phase, a circulatory phase, or a metabolic phase. The oneor more output devices can present a visual or audible feedback based onthe generated transform values and the previous values. The feedbackincludes an indication of a likelihood of success from delivering adefibrillating shock. The future therapeutic action or the phase of thecardiac event can be generated based on one or more additionalparameters. The one or more additional parameters can include at leastone of: trans-thoracic impedance (TTI), levels of prior successfuldefibrillations, and a trend in AMSA values over time.

The transform values can include amplitude spectrum area (AMSA) values.The therapeutic action can be determined based on determining a trendingof the transform values in the time series. The transform values caninclude normalized transform values. The transform can include a FastFourier Transform. The transform can include one or more of: Fourier,discrete Fourier, Hilbert, discrete Hilbert, wavelet, and discretewavelet methods. The transform can be a transform that uses zerocrossing analysis.

In one implementation, a system for managing care of a person receivingemergency cardiac assistance is disclosed. The system comprises one ormore capacitors for delivering a defibrillating shock to a patient; oneor more electronic ports for receiving signals from sensors forobtaining indications of an electrocardiogram (ECG) for the patient; anda patient treatment module executable on one or more computer processorsto provide a determination of a likelihood of success from delivering afuture defibrillating shock to the person with the one or morecapacitors, using (a) information about a prior defibrillating shock,and (b) a value that is a function of current ECG signals from thepatient. The system can also include an output mechanism arranged toindicate, to a user of the system, an indication regarding thelikelihood of success from delivering a defibrillating shock to theperson with the one or more capacitors. The output mechanism can includea visual display, and the system can be programmed to display to theuser one of multiple possible indications that each indicate a degree oflikelihood of success. Alternatively or in addition, the outputmechanism can comprise an interlock that prevents a user from deliveringa shock unless the determined likelihood of success exceeds a determinedvalue.

In some aspects, the patient treatment module comprises an ECG analyzerfor generating an amplitude spectrum area (AMSA) value, wherein thepatient treatment module uses the information about the level of successfrom the prior defibrillating shock to adjust the AMSA value. Moreover,the patient treatment module can comprise an ECG analyzer for generatingindications of heart rate for the patent, heart rate variability for thepatent, ECG amplitude for the patent, and/or first or second derivativesof ECG amplitude for the patent. The indication of ECG amplitude cancomprise, for example, an RMS measurement, measure peak-to-peak,peak-to-trough, or an average of peak-to-peak or peak-to-trough over aspecified interval

In other aspects, the patient treatment module is programmed todetermine whether a prior defibrillation shock was at least partiallysuccessful, and based at least in part on the determination of whetherthe prior defibrillation was at least partially successful, modify acalculation of the likelihood of success from delivering the futuredefibrillating shock. Moreover, determining a likelihood of success fromdelivering a future defibrillating shock to the person can depend on adetermination of whether one or more prior shocks delivered to theperson were successful in defibrillating the person. In addition,determining a likelihood of success from delivering a futuredefibrillating shock can comprise performing a mathematical transform onthe ECG data. The mathematical transform can be selected from a groupconsisting of Fourier, discrete Fourier, Hilbert, discrete Hilbert,wavelet, and discrete wavelet methods. In some implementations, thedetermination of the likelihood of success can include a zero-crossingbased analysis, an example of which is described in Kedem, SpectralAnalysis and Discrimination by Zero-Crossings, Proceedings of the IEEE,Vol. 74, No 11, November 1986. Zero-crossing counts in filtered timeseries can be referred to as higher order crossings. In addition,determining a likelihood of success from delivering a futuredefibrillating shock comprises performing a calculation by an operationselected from a group consisting of logistic regression, table look-up,neural network, and fuzzy logic.

In yet another example, the patient treatment module is programmed todetermine the likelihood of success from delivering a futuredefibrillating shock using at least one patient-dependent physicalparameter separate from a patient ECG reading. The patient treatmentmodule can also be programmed to determine the likelihood of successfrom delivering a future defibrillating shock using at a measure oftrans-thoracic impedance of the person.

In another implementations, a method for managing care of a personreceiving emergency cardiac assistance is disclosed, and comprisesmonitoring, with an external defibrillator, electrocardiogram (ECG) datafrom a person receiving emergency cardiac assistance; determiningwhether a prior defibrillation shock occurred; determining a likelihoodof future defibrillation shock success using at least the ECG data;based at least in part on the determination of whether the priordefibrillation occurred, modifying the calculation of the chance ofdefibrillation shock success; and affecting control of the externaldefibrillator based on the identification of whether a presentdefibrillation shock can likely be effective. Determining a likelihoodof future defibrillation shock success can comprise determining a valuethat is a function of electrocardiogram amplitude at particulardifferent frequencies or frequency ranges. Determining a likelihood offuture defibrillation shock success can comprise determining anamplitude spectrum area (AMSA) value for the ECG data, and can alsocomprise adjusting the determined AMSA value using information about theprior defibrillation shock. In addition, the method can comprisedetermining whether the adjusted AMSA value exceeds a predeterminedthreshold value.

In some implementations, the method comprises providing to the rescuer avisual, audible, or tactile alert that a shockable situation exists forthe person, if the adjusted AMSA value is determined to exceed thepredetermined threshold value. The method can also include determiningwhether a prior defibrillation shock was at least partially successful,and based at least in part on the determination of whether the priordefibrillation was at least partially successful, modifying acalculation of the likelihood of success from delivering the futuredefibrillating shock. The determining of a likelihood of success fromdelivering a future defibrillating shock can comprise performing amathematical transform on the ECG data, and the mathematical transformcan be selected from a group consisting of Fourier, discrete Fourier,Hilbert, wavelet, and discrete wavelet methods. Also, determining alikelihood of success from delivering a future defibrillating shock cancomprise performing a calculation by an operation selected from a groupconsisting of logistic regression, table look-up, neural network, andfuzzy logic. Moreover, the likelihood of success from delivering afuture defibrillating shock can be determined using at least onepatient-dependent physical parameter separate from a patient ECGreading.

In some implementations, the additional physiologic parameter istrans-thoracic impedance of the person receiving emergency cardiac care,and the indication of trans-thoracic impedance can be determined fromsignals sensed by a plurality of electrocardiogram leads that alsoprovide the EGC data. The method can also include cyclically repeatingthe actions of monitoring, determining, identifying and providing theindication. The method also can comprise identifying compression depthof chest compressions performed on the person, using a device on theperson's sternum and in communication with the external defibrillator,and providing feedback to a rescuer performing the chest compressionsregarding rate of compression, depth of compression, or both.

In yet another implementation, there is disclosed a system for managingcare of a person receiving emergency cardiac assistance that comprisesone or more capacitors for delivering a defibrillating shock to apatient; one or more electronic ports for receiving signals from sensorsfor obtaining indications of an electrocardiogram (ECG) for the patient;and a patient treatment module executable on one or more computerprocessors to identify an phase in which a patient being monitored bythe system is in relative to a time at which an adverse cardiac eventfor patient began. The phase in which the patient being monitored by thesystem is in can includes an elapsed time since the adverse cardiacevent for the patient began, and a phase selected from an electrical,circulatory, and metabolic phase. The system can also comprise an outputmechanism arranged to indicate, to a user of the system, an indicationregarding the phase in which the patient is in. The output mechanism cancomprise a visual display, and the system can be programmed to displayto the user one indication of multiple possible indications, wherein theone indication indicates to the user the phase in which the patient isin.

In some implementations, the system is programmed to displayinstructions for the user to care for the patient, the instructionsselected to correspond to the phase in which the patient is in. Also,the output mechanism can include an interlock that prevents a user fromdelivering a shock unless a determined likelihood of success of a shockreviving the patient exceeds a determined value. In other aspects, thepatient treatment module comprises an ECG analyzer for generating anamplitude spectrum area (AMSA) value, an indication of heart rate forthe patent, an indication of heart rate variability for the patent, oran indication of ECG amplitude for the patent.

In yet other aspects, the indication of ECG amplitude comprises an RMSmeasurement, measured peak-to-peak, peak-to-trough, or an average ofpeak-to-peak or peak-to-trough over a specified interval. Also, thepatient treatment module can include an ECG analyzer for generating anindication of a first derivative of ECG amplitude for the patent, or anindication of a second derivative of ECG amplitude for the patent.Moreover, the patient treatment module can be programmed to determinewhether a defibrillation shock, prior to a future defibrillation shockbeing consider for delivery, was at least partially successful, andbased at least in part on the determination of whether the priordefibrillation shock was at least partially successful, modifying acalculation of a likelihood of success for delivering the futuredefibrillation shock.

In another implementation, a method for managing care of a personreceiving emergency cardiac assistance is disclosed and comprisesmonitoring, with an external defibrillator, electrocardiogram (ECG) datafrom a person receiving emergency cardiac assistance; performing amathematical transform of the ECG data from a time domain to a frequencydomain using a tapered window in the time domain; determining alikelihood of future defibrillation shock success using at least themathematical transformation; and affecting control of the externaldefibrillator based on the identification of whether a presentdefibrillation shock can likely be effective. The tapered window cancomprise a Tukey window, and can be between about one second and about 2seconds wide. The tapered window can be selected from a group consistingof Tukey, Hann, Blackman-Harris, and Flat Top, and the mathematicaltransform can comprise a Fast Fourier Transform.

In some implementations, determining a likelihood of futuredefibrillation shock success comprises determining a value that is afunction of electrocardiogram amplitude at particular differentfrequencies or frequency ranges. It can also comprise determining anamplitude spectrum area (AMSA) value for the ECG data. Also, determininga likelihood of future defibrillation shock success can further compriseadjusting the determined AMSA value using information about a priordefibrillation shock. Moreover, the method can additionally includedetermining whether the adjusted AMSA value exceeds a predeterminedthreshold value. In some aspects, the method also includes providing toa rescuer a visual, audible, or tactile alert that a shockable situationexists for the person receiving emergency cardiac assistance, if theadjusted AMSA value is determined to exceed the predetermined thresholdvalue.

In yet other aspects, the method comprises determining whether a priordefibrillation shock was at least partially successful, and based atleast in part on the determination of whether the prior defibrillationwas at least partially successful, modifying a calculation of thelikelihood of success from delivering the future defibrillating shock.In some implementations, determining a likelihood of success fromdelivering a future defibrillating shock comprises performing acalculation by an operation selected from a group consisting of logisticregression, table look-up, neural network, and fuzzy logic. Thelikelihood of success can also be determined using at least onepatient-dependent physical parameter separate from a patient ECGreading, and the additional patient-dependent parameter can comprise anindication of trans-thoracic impedance of the person receiving emergencycardiac care.

In additional aspects, the indication of trans-thoracic impedance isdetermined from signals sensed by a plurality of electrocardiogram leadsthat also provide the EGC data. The method can also comprise cyclicallyrepeating the actions of monitoring, determining, identifying andaffecting the control, and can also or alternatively include identifyingcompression depth of chest compressions performed on the personreceiving emergency cardiac assistance, using a device on the person'ssternum and in communication with the external defibrillator, andproviding feedback to a rescuer performing the chest compressions, thefeedback regarding rate of compression, depth of compression, or both.Also, the affecting control can include preventing a user fromdelivering a shock unless the determination of whether a shock can beeffective exceeds a determined likelihood level, and/or electronicallydisplaying, to a user, an indicator of the determined indication ofwhether a shock can be effective. In addition, displaying an indicatorcan include displaying a value, of multiple possible values in a rangethat indicates a likelihood of success. Moreover, the calculation of thelikelihood of current shock success can be determined or modified usinga determination of a value of trans-thoracic impedance of the person.

In some implementations, a system is provided that includes one or moreelectronic ports for receiving signals from sensors for obtaining a timedomain electrocardiogram (ECG) of the patient, and a patient treatmentmodule comprising an ECG analyzer and a non-transitory computer-readablestorage medium encoded with a computer program comprising instructionsthat, when executed, cause one or more processors to perform a number ofoperations. The operations can include performing at least onetransformation of at least a portion of the time domain ECG signal fromthe patient into frequency domain data, determining a firstfrequency-based value over a first evaluation period based on the atleast one transformation, determining a second frequency-based valuerepresenting a trend over a second evaluation period based on the atleast one transformation, determining a probability of therapeuticsuccess based at least in part on the first frequency-based value andthe second frequency-based value, and providing an indication of theprobability of therapeutic success.

Other features and advantages will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A shows schematically the combination of various types of data inmaking a determination about likely effectiveness of a defibrillatingshock.

FIG. 1B shows a victim of a cardiac event being treated with an exampleportable defibrillator.

FIG. 1C is a graph that represents example changes in AMSA during anevent correlated to phases in the event.

FIG. 1D is a table showing examples relating AMSA to predictedlikelihood of failure in defibrillating a victim who has or has not beenpreviously defibrillated.

FIG. 1E is a schematic diagram of an example data structure forcorrelating AMSA and defibrillation success to predicted outcomes forshocking a victim.

FIG. 1F is an example table showing predictions of successfuldefibrillation for different AMSA threshold values in the instances of1^(st) defibrillation attempts.

FIG. 1G is an example table showing AMSA prior defibrillation forrefractory and recurrent VF.

FIG. 1H is an example table showing prediction of successfuldefibrillation for increasing AMSA threshold values in the instances ofrefractory VF.

FIG. 1I shows examples of window functions and resulting FFTs from thosefunctions.

FIG. 1J is an example graph of area under curve for different windows.

FIG. 1K is an example graph of post-shock rhythm for different AMSAranges.

FIG. 1L is a chart of AMSA values and statistics.

FIG. 1M is an example display including ECG, AMSA and CPRrepresentations.

FIG. 1N is another example display including an AMSA representation.

FIG. 1O is another example display including an AMSA representation.

FIG. 1P is an example defibrillation dose-response curve.

FIG. 1R is a representation of defibrillation success rate as functionof AMSA.

FIG. 1Q is an example table showing prediction of successfuldefibrillation for each mVHz change in AMSA.

FIG. 1S is an example graphical representation showing prediction ofsuccessful defibrillation for each mVHz change in AMSA.

FIG. 1T is an example display including an FFT representation.

FIG. 1U is an example of where a change in AMSA is monitored during thecourse of CPR.

FIG. 2 is a schematic block diagram that shows a defibrillator with anelectrode package and compression puck.

FIG. 3A is a flow chart of an example process for providing guidance toa rescuer.

FIG. 3B is a flow chart of another example process for providingguidance to a rescuer.

FIGS. 4A and 4B are graphs showing relationships between patient outcomeand AMSA threshold values for groups of patients having differenttrans-thoracic impedance values.

FIGS. 5A and 5B illustrate a defibrillator showing examples ofinformation that can be displayed to a rescuer.

FIGS. 6A-6C show screenshots of a defibrillator display that providesfeedback concerning chest compressions performed on a victim.

FIGS. 7A and 7B show screenshots providing feedback regarding aperfusion index created from chest compressions.

FIGS. 8A and 8B show screenshots with gradiated scales indicating targetchest compression depths.

FIG. 9 shows a general computer system that can provide interactivitywith a user of a medical device, such as feedback to a user in theperformance of CPR.

DETAILED DESCRIPTION

The present disclosure generally relates to the use of changes or trendsin spectral frequency (e.g., AMSA, FFT) in evaluating the likelihoodthat an electrical shock will lead to a successful therapeutic result(e.g., defibrillation). For example, when the AMSA or otherfrequency-based data is greater than a certain threshold, the percentageof shock success can be sufficiently high such that a caregiver ormedical apparatus can make a decision to administer an electrical shock.Alternatively, for relatively low values of AMSA or otherfrequency-based data, observed changes in frequency-based data can be asubstantial contributor to the overall percentage of shock success.Changes in spectral frequency of an ECG can provide further information(in addition to the actual values of the spectral frequency analysis),which can beneficially lead to a therapeutic shock at an earlier time,for example, as compared to a case where only the actual values of thespectral frequency are taken into account. Accordingly, by implementingsystems and methods described herein, patients can be able to receivelife-saving therapies quickly and effectively.

In some implementations, a therapeutic system can be configured toperform a number of operations. For example, the therapeutic system caninclude a processor configured to receive signals from sensors to obtaina time domain ECG of a patient, and can further analyze the time domainECG. Such analysis can include performing a number of time-frequencytransformations of multiple portions of the time domain ECG signal fromthe patient into frequency domain data. Based on the time-frequencytransformation(s), the processor can determine a first frequency-basedvalue (e.g., FFT of the ECG data or an AMSA value) over a firstevaluation period, and a second frequency-based value representing atrend over a second evaluation period (e.g., upward trend in FFT of theECG data or in AMSA), where the two evaluation periods can or cannotoverlap. Based on these two frequency-based values, the processor canthen calculate or otherwise determine (e.g., based on a logisticregression, a threshold based determination, or any other appropriatemethod) a probability that a particular type of therapy can lead to asuccessful patient outcome.

The system can then provide an indication of the probability of successto an operator and/or treatment apparatus, for making a decision ofwhether or not to administer the therapy.

In general, defibrillation is a common treatment for variousarrhythmias, such as VF. However, the deliverance of an electrical shockcan generate several side effects (e.g., heart tissue damage, skinburns, etc.). Electric shock therapy can require interruptions of chestcompressions during the deliverance of the shock. Additionally, theeffectiveness of defibrillation can decrease over the elapsed time of anepisode—where an episode can be measured from the time when a victimfirst starts feeling symptoms of a cardiac event (e.g., VF) or losesconsciousness. Generally, the time from onset of a VF episode andunconsciousness is relatively short, in the order of tens of seconds.For any given period of time during a cardiac event, it is desirable topredict whether defibrillation can be successful in restoring a regularheartbeat following the onset of an arrhythmic episode, so that suitablelevels of shock are administered at appropriate times. It can also behelpful to determine how long it has been since a cardiac event startedor in which metabolic stage the patient is in (e.g., a first, second, orthird metabolic stage or phase). The techniques described in thisdocument can be used to better predict when a defibrillation shock canbe successful and whether to administer treatment at earlier times thanrecommended by standard, non-personalized protocol. Because the windowof time is typically very short, a personalized treatment including theidentification of an optimal moment to generate a defibrillation shockcan increase the probability that the person experiencing arrhythmiawill survive.

Such predictions can each be referred to as an “indicator of success”or, equivalently, a “success indication” within the context of thepresent disclosure. The determined prediction can be associated with amyocardial viability metric, where myocardium is considered to be viableif during a cardiac event (e.g., VF) it has the potential to recover itsfunction. The prediction can be used so that a defibrillating shock isnot provided when the chance of successful defibrillation is low (e.g.,the myocardium is not viable), and instead defibrillation is postponeduntil the chance of successful defibrillation increases to an acceptablelevel; until such a time, a rescuer can be instructed to provide othercare such as regular chest compressions, forceful chest compressions, orother cardiac assistance procedures.

Such a determination about likelihood of successful shock can be used toenhance personalized care in an automatic and/or manual defibrillationprocedure. In an automatic procedure, a defibrillator can be designed tocondition the generation of defibrillation shocks based on apredetermined threshold of a success metric. In a manual procedure, thesuccess indication can be shown to a rescuer, and the rescuer candetermine whether to apply a shock or not based on the indication, orthe system can provide other information to the rescuer. For example,the indication of success can show a percentage likelihood for a shockto succeed, or can be a less specific indicator, such as an indicationof which phase (e.g., of three phases discussed above and below) thevictim is currently in, so that the rescuer can immediately understand,from experience and training related to those phases, thatdefibrillation attempts are likely to be successful or not.

Additional information provided to a rescuer can take the form ofinstructions, such as instructions to perform chest compressions or someother action, where the action is selected from among a plurality ofpossible treatments based on the current phase for the victim. A systemcan also integrate both (e.g., locking out the ability to provide ashock until a threshold level is reached, and then showing the relativelikelihood of success above that value). The likelihood or probabilityof success can be provided in various manners, such as quantitatively(e.g., by showing an actual percentage), or qualitatively (e.g., showingtwo or more of a low, medium, or high likelihood of success on anelectronic display of a defibrillator).

In certain implementations described herein, the present disclosure isdirected to systems and methods for predicting whether defibrillationcan be effective using amplitude spectrum area (AMSA) or any otherappropriate Shock Prediction Algorithms (SPA) using analysis of ECGdata, and adjusting such SPA predictions based on either the existenceof prior defibrillation shocks as well as observations of a patient'sreaction to those defibrillating shocks. In particular, it has beenobserved that victims of cardiac fibrillation can successfullydefibrillate for lower AMSA threshold values if they have beenpreviously successfully defibrillated during the same rescue session.Thus, rather than treating each shock as a discrete event in analyzingthe probability of success, the techniques described here take intoaccount prior shock deliveries, and an observed response of the patientto those deliveries, in determining an AMSA value or other value thatcan indicate that a shock currently applied to the patient can likely besuccessful (or not) in defibrillating the patient. Such a determinationcan also be combined with determinations about trans-thoracic impedance(trans-thoracic impedance) of the patient, as discussed more fullybelow.

To obtain better predictive value for the AMSA values, the time windowfrom which the ECG data for an AMSA determination is taken can be maderelative small (e.g., between 3 and 4 seconds, between 2 and 3 seconds,and between 1 and 2 seconds), which can place the data as close to thecurrent status of the patient as possible. Smaller windows can sufferfrom edge effects more-so than larger windows, so the shape andcoefficients for the windows can also be selected to maximize predictivepower of the method. For example, a Tukey window having appropriatecoefficients, such as about 0.2, can be employed.

FIG. 1A shows schematically an example combination 100A of various typesof data in determining the probability of a defibrillating shocksuccess. In a particular implementation one of the data types can beused alone, or multiple data types can be combined to generate acomposite myocardial viability metric (e.g., by giving a score to eachtype and a weight, and combining them all to generate a weightedcomposite score for a likelihood). In this example, a shock indication116 is the outcome of a decision process that can be performed by adefibrillator alone or in combination with one or more pieces ofancillary equipment (e.g., a computing device such as a smartphonecarried by a healthcare provider). The shock indication 116 can beprovided to a part of the defibrillator (e.g., via an analog or digitalsignal that represents the indication, so that the receiving part of thedefibrillator can cause a shock feature to be executed or to cause it tobe enabled so that it can be manually executed by an operator of thedefibrillator). The shock indication can also or alternatively beprovided to a rescuer (e.g., can be displayed by a defibrillator) so asto indicate that a defibrillating shock can be delivered. In the contextof this disclosure, a defibrillating shock is an electrical shockdesigned to cause cardiac defibrillation, independent of whether itcauses a successful defibrillation or not.)

The relevant inputs can obtain at least some of their data from signalsgenerated by a pair of electrodes 102 that can be adhered to a patient'storso—above one breast and below the other, for example, in a typicalmanner. The electrodes can include leads for obtaining ECG data andproviding such data for analysis for a number of purposes. In addition,a CPR puck 104 can be placed on a patient's sternum and can deliversignals indicative of acceleration of the puck, and thus of up-downacceleration of the patient's sternum, which can be integrated so as toidentify a depth of compression by the rescuer (and can also be used toidentify whether the patient is currently receiving chest compressionsor not).

In some implementations, the shape of the window can be asymmetric. Forinstance, the edge of the window that is “older” in time can have awindow shape that results in a greater level of attenuation that doesthe “newer” portion of the windowed data. Other asymmetric shapes canalso be used, as appropriate, to generate data that best represents anaccurate prediction of shock success.

The electrodes 102 can be electrically connected to an ECG unit 106,which can be part of a portable defibrillator and can combine data fromdifferent leads (e.g., 8 leads) in a familiar manner to construct asignal that is representative of the patient's ECG pattern. Such an ECGsignal is often used to generate a visual representation of thepatient's ECG pattern on a screen of the defibrillator. The ECG-relateddata can also be analyzed in various ways to learn about the currentcondition of the patient, including in determining what sort of shockindication to provide to control the defibrillator or to display to arescuer.

As one such example, ECG data can be transformed from the time domaininto frequency domain data, for example by using FFT module 107. The FFTmodule 107 can nearly continuously and repeatedly compute a set offrequency-based values, a numeric value or a similar indicator thatrepresents a frequency amplitude at particular different times and/orfrequency ranges corresponding to changes during a particular timeinterval. The frequency domain data can be used to generate a myocardialviability metric and/or it can be used as an input for AMSA analyzer108. AMSA analyzer 108 can nearly continuously and repeatedly compute anAMSA number, a change in AMSA over time, a change in rate of AMSArelative to time and/or a similar indicator that represents ECGamplitude at particular different frequencies and/or frequency ranges inan aggregated form (e.g., a numeral that represents a value of theamplitude across the frequencies). Generally, the goal is to identify awaveform in which amplitude of the VF signals is large, and inparticular, relatively large in the higher frequency ranges. Similarly,power spectrum area can be measured and its change over time can also beused as an input that is alternative to, or in addition to, a changeover time in AMSA value for purposes of making a shock indication. Asdescribed in more detail above and below, a current AMSA value and/or achange over time in AMSA value can be used to determine whether a shockis likely to be successful. A plurality of combined AMSA values, such asa running average computed several times during a particular timeinterval (and each covering a time period longer than the time periodfor the first AMSA value) using a moving window can indicate how muchtime has elapsed since a cardiac event began. The estimation of theonset of the cardiac event can indicate which phase, of multiplemetabolic phases during a VF event, the victim is in. Each metabolicphase is associated with a different most-effective treatmentsub-protocol. Also, when rescuers first arrive on a scene, severalseconds of ECG data can be used to provide them an initial indication ofthe time since the event started and/or the phase in which the victimcurrently is in (e.g., by displaying a number of elapsed minutes or thename of one of multiple phases on a display screen of a medical devicesuch as a monitor or defibrillator/monitor).

The AMSA analyzer 108 can be programmed to perform the analysis of theECG, and perhaps other, inputs so as to maximize the predictive value ofthe AMSA value, whether by affecting inputs to the AMSA determination,and/or making an AMSA determination and then adjusting the AMSA valuethat is generated from that determination. As one example, the size ofthe window from which ECG data is taken in making the calculation can beset to maximize the predictive value, such as by being about 1 second toabout 1.5 seconds long. As another example, the shape of the window canbe tapered, such as by being in the form of a Tukey or Hann window,rather than having vertical edges like a boxcar window. Similarly, thecoefficients for the window, such as Chi2 and p can be set to maximizethe expected predictive value of the calculation. The AMSA analyzer canalso be programmed to change such values dynamically over the course ofa particular VF incident, either by moving the values progressively astime elapses so as to make the values match known expected values formaximizing the predictive effect of the calculation, or to respond toparticular readings, e.g., to use particular window length, form, orcoefficients when an AMSA value is in a pre-defined range.

A trans-thoracic impedance module 110 can also obtain information fromsensors provided with the electrodes 102, which indicates the impedanceof the patient between the locations of the two electrodes. Theimpedance can also be a factor in determining a shock indication asdescribed in more detail below.

A defibrillation history success module 112 tracks the application ofdefibrillating shocks to the patient and whether they were successful indefibrillating the patient, and/or the level to which they weresuccessful. For example, the module 112 can monitor the ECG waveform intime windows of various sizes for a rhythm that matches a profile of a“healthy” heart rhythm, and if the healthy rhythm is determined to beestablished for a predetermined time period after the application of adefibrillating shock, the module 112 can register the existence of asuccessful shock. If a shock is applied and a healthy rhythm is notestablished within a time window after the delivery of the shock, themodule 112 can register a failed shock. In addition to registering abinary value of success/fail, the module can further analyze the ECGsignal to determine the level of the success or failure and may, forexample, assign a score to the chance of success of each shock, such asa normalized score between 0 (no chance of success) and 1 (absolutecertainty).

A CPR chest compression module 114 can receive signals about the motionof the puck 104 to determine whether chest compressions are currentlybeing applied to the patient, and to determine the depth of suchcompressions. Such information can be used, for example, in giving arescuer feedback about the pace and depth of the chest compressions(e.g., the defibrillator could generate a voice that says “pushharder”). The presence of current chest compression activity can alsosignal the other components that a shock is not currently advisable, orthat ECG data should be analyzed in a particular manner so as to removeresidual artifacts in the ECG signal from the activity of the chestcompressions.

Information about pharmacological agents 115 provided to a patient canalso be identified and taken into account in providing a shockindication to a rescuer. Such information can be obtained manually, suchas by a rescuer entering, via a screen on a defibrillator or on a tabletcomputer that communicates with the defibrillator, identifiers for thetype of agent administered to a patient, the time of administration, andthe amount administered. The information can also be obtainedautomatically, such as from instruments used to administer theparticular pharmacological agents. The device that provides a shockindication can also take that information into account in identifyingthe likelihood that a shock can be successful if provided to the patient(e.g., by shifting up or down an AMSA threshold for measuring shocksuccess likelihood), and for other relevant purposes.

One or more of the particular factors discussed here can then be fed toa shock indication module 116, which can combine them each according toan appropriate formula so as to generate a binary or analog shockindication. For example, any of the following appropriate steps can betaken: a score can be generated for each of the factors, the scores cannormalized (e.g., to a 0 to 1 or 0 to 100 scale), a weighting can beapplied to each of the scores to represent a determined relevance ofthat factor to the predictability of a shock outcome, the scores can betotaled or otherwise combined, and an indication can be determined suchas a go/no go indication, a percentage of likely success, and other suchindications.

In this manner then, the system 100 can take into account one or aplurality of factors in determining whether a shock to be delivered to apatient is likely to be successful. The factors can take data measuredfrom a plurality of different inputs (e.g., ECG, trans-thoracicimpedance, delivered agents, etc.), and can be combined to create alikelihood indication, such as a numerical score that is to be measuredagainst a predetermined scale (e.g., 0 to 100% likelihood or A to Fgrade). Such determination can then be used to control anautomatically-operated system (e.g., that delivers chest compressionsmechanically), to limit operation of a manually-operated system (e.g.,by enabling a shock that is triggered by a user pressing a button), orby simply providing information to a system whose shock is determinedsolely by a rescuer (e.g., for manual defibrillators in which theoperator is a well-trained professional).

FIG. 1B shows an example of a configuration 100B including a victim 122of cardiac arrest being cared for by a rescuer using a defibrillator124. The defibrillator 124 includes an electrode package 126 and acompression puck 128 generally coupled thereto. An example of such adefibrillator includes the AED PLUS automated external defibrillator orthe AED PRO automated external defibrillator, both from ZOLL MedicalCorporation of Chelmsford, Mass. Other embodiments of the defibrillator124 are possible.

In the pictured example, the victim 122 is rendered prone due to anarrhythmic episode, and the electrode package 126 and the compressionpuck 128 are positioned on the torso of the victim 122 in an appropriateand known arrangement. In accordance with the present disclosure, thedefibrillator 124, in tandem with one or both of the electrode package126 and the compression puck 128, is configured to determine whether adefibrillation shock can be an effective measure to terminate thearrhythmic episode. The determination is generally based on priorsuccess or failure of defibrillating shocks, one or more trans-thoracicimpedance measurements, and one or more calculated changes in AMSA valueover time. As shown in the figure, the patient 122 is shown at twopoints in time—(a) point t₁ at which the patient has been defibrillatedand is shown with his eyes open and a healthy ECG pattern 135A toindicate such successful defibrillation, and (b) at a later time t₂,when the patient has refibrillated and is shown with closed eyes torepresent such a state, and with an erratic ECG trace 135B.

The defibrillator 124 is configured to acquire and manipulate both atrans-thoracic impedance signal 130 and an ECG signal 132 via theelectrode package. As described in further detail below, atrans-thoracic impedance measurement (0) is a parameter derived from thetrans-thoracic impedance signal 130 that represents, among other things,thoracic fluid content. An AMSA value (mVHz) is a parameter calculatedby integrating the Fourier transform of the ECG signal 132 over a finitefrequency range. The AMSA value is one form of calculation thatrepresents a value of an ECG signal from a victim, while other SPAvalues can likewise be computed.

The defibrillator 124 is further configured to display an indicator134A/B based on the defibrillating history (determined from ECG data),trans-thoracic impedance measurement(s) and AMSA value(s) obtained fromthe ECG signal 132, trans-thoracic impedance signal 130 and an ECGsignal 132, respectively. The indicator 134A/B generally provides aperceptible cue that suggests whether or not a particular defibrillationevent can likely terminate the arrhythmic episode of the victim 122. Forexample, for the victim 122 at time t1, the indicator 134A displays an Xto indicate that no shock should be delivered to the victim 122. Incontrast, at time t2, the indicator 134B displays a success indicationof “88%,” so a rescuer (not shown) can be instructed “Press to Shock,”so as to apply a shock to the victim 122 via actuation of a control 137(e.g., a button that the user can actuate).

In this situation, the indication of an 88% likelihood of success wasmade by consulting data structure 130, which can be stored in memory ofdefibrillator 124 upon analysis that occurred around the time of t1, andapplying an appropriate calculation to data from the data structure 130.In particular, the defibrillator can analyze ECG data and an indicatorprovided by shock delivery circuitry in order to determine that a shockwas delivered, and at a time soon after, the patient's heart rhythmentered a normal pattern, such that the defibrillator 123 can determinethat the shock was a success at time t1. Upon making such adetermination, the defibrillator can update data structure 130 toindicate that a successful defibrillation event has occurred during therescue attempt. Other shocks can also be delivered, and the datastructure 130 can be updated to reflect such events, and the success orfailure of such events.

Data structure 130 or another data structure can also store informationabout prior AMSA readings for the victim during the particular VFepisode. For example, a separate AMSA measurement and calculation can bemade periodically (e.g., multiple times each second, once each second,or once every several seconds) and at least some past calculated AMSAvalues can be stored in data structure 130. Such values can be combined,and determinations can be made about general values (with lowvariability because of the combining) and trends in AMSA values, wheresuch determination can indicate information such as the progress of thevictim through phases that are generally indicative of the likelihood ofsuccess of particular actions taken on the victim by a rescuer.Moreover, such information can be used to generate an indication to arescuer of the elapsed time (approximate) since the victim entered VF,or an indication of the phase the victim is currently in, among otherthings.

Embodiments other than those that display percentage likelihood for ashock indication are possible for the one likelihood indicationdiscussed here. For example, it can be appreciated that a successindication can be implemented as any appropriate type of perceptiblefeedback (e.g., haptic, audio, etc.) as desired. Two simultaneousindications can also be provided, where both can be the same style ofindication (e.g., visual display) or different types (e.g., visualdisplay for one and haptic for the other)—e.g., the phase in which avictim is currently located can be displayed on a screen of adefibrillator, while a current AMSA value indicating a relatively highchance of success can be communicated by vibration of or display on apuck on which the rescuer has placed his hands (so as to encourage therescuer to back-off and provide the shock).

In some implementations, the defibrillator 124 can make thedetermination of a likelihood of success without expressly notifying therescuer, and can simply use the determination to determine when to tellthe rescuer that a shock can be delivered, or to provide otherinstructions to a rescuer. In other situations, the defibrillator 124can explicitly indicate the likelihood of success, such as by showing apercentage likelihood, by showing less discrete gradients for success(e.g., poor, good, very good, and excellent), or by displaying a rangeof colors (e.g., with red indicating a poor chance and green indicatinga good chance). The type of indication that is displayed can also differbased on a mode in which the defibrillator 124 is operating—for example,in a professional mode, more detailed information can be provided,whereas in an AED mode, simpler information (a “go”/“no go” choice) canbe presented.

In such manner then, the defibrillator can conduct a number ofrelatively complex calculations and can combine multiple factors indetermining whether to allow a shock to be provided to a patient, or toencourage the application of such a shock by a rescuer.

FIG. 1C is a graph 100C that represents changes in AMSA during a VFevent correlated to phases in the event. In general, the graph 130 showshow AMSA varies along with variations in a patient ECG, and varies moregenerally over a longer time period by decreasing over time after theevent has started.

The time across this graph can be, for example, about 15 minutes. Thetime is broken into three phases. A defibrillation phase 133 canrepresent about the first 4 minutes (plus or minus one minute) of theevent. A deep CPR phase 134 can run from about four minutes to about 10minutes after onset of the event. And an Other CPR phase 136 canrepresent the remainder of the event, assuming the victim has not beenrevived by that time.

Line 138 is represented as being drawn through all of the AMSA valuescomputed periodically throughout the time of the event. The line isshown as linearly decreasing for clarity, though AMSA generallydecreases exponentially. If AMSA were graphed for a rescuer, it could beshown as an exponential curve, as a line on an exponential scale, and/orwith error bars showing statistical variation in the readings. As can beseen, the AMSA values vary up and down (with a general downward trendover time), and such variation represents changes in the victim's ECGwhere the changes can represent changes in likelihood that a shock,currently delivered, can be successful. But although there is relativelylarge variation over short time periods, the variation is less overlonger time windows, such as over 10 or more seconds. Thus, for example,AMSA values can be computed periodically over a short time period, andmore general values can be computed by averaging or otherwise combiningthe individual measurements. A running average is represented by line140. Line 140 can simply represent the average of past computations, andcan also be extended into the future in some implementations, such as bylinear regression or other appropriate statistical techniques. Forpurposes of clarity, the overall AMSA value is shown here as decreasinglinearly with time, though the actual variation can differ from what isshown here.

In this example, two points on line 140 are particularly relevant,points 142 and 144. These points represent locations at which thecombined AMSA value measurement (e.g., averaged over a window of time)decrease below a predetermined value. For example, the value for point142 can have been selected from observations of ECG data, andcorresponding AMSA values from data captured for actual real-worldresuscitation events with real victims, and such data can indicate thatresuscitation from shock decreases below an acceptable value and/ordecreases off more quickly upon passing below a particular AMSA value.Such AMSA value can be selected as a cut-off point that defines the linebetween the first phase and the second phase. Similarly, such data canindicate that chest compressions or a particular type of chestcompressions, such as forceful chest compressions, fell below aparticular level of effectiveness or changed relatively rapidly in theireffectiveness past another AMSA value. As such, point 144 can representan AMSA value determined from such data analysis to correspond to suchchanges as observed across the large population of VF events. The points142, 144 are mapped to the determined values with horizontal dottedlines, and a defibrillator or other device can monitor the combined AMSAvalue as an event progresses so as to identify when the predeterminedAMSA value is reached. A similar monitoring can be employed with respectto identifying the existence of point 144.

Each of the points 142, 144 is also mapped to the time axis,representing the time at which the particular victim was determined tohave transitioned from one phase to another. Generally, the times can berelatively similar as between different victims and different cardiacevents, where the changes are driven in large part by ischemic effectsthat the event has on the heart tissue. At such points in time for theparticular victim represented by this graph, the behavior of a medicaldevice such as a defibrillator that is treating the victim can change inthe ways discussed above and below.

As such, the device can determine an estimated time since the VF eventbegan using AMSA values and/or other information, where particular AMSAvalues from a studied population have been determined to correspond toparticular times since collapse or other instantiation of the VF event.Such information can be displayed in real-time or stored, such as todetermine response times, and to perform studies on effectiveness ofrescuers as a function of the time since initiation of the event when adefibrillator is first connected and operable for the victim.

Example A

As for particular AMSA values for use in defining points 142 and 144,one example can be instructive. Data from an Utstein-compliant registryalong with electronic ECG records were collected on consecutive adultnon-traumatic OHCA patients treated by 2 EMS agencies over a 2 yearperiod. Patients with bystander witnessed CA and with VF as initial CArhythm were included (n=41). AMSA was calculated in earliest pausewithout compression artifacts, using a 2 second ECG with a Tukey (0.2)FFT window. VF duration was calculated as the sum of the time intervalfrom collapse to defibrillator on and the time interval fromdefibrillator on to first CPR interruption for defibrillation delivery.

VF duration ranged between 6.5 and 29.6 min (11.3+4.1 min), with acorresponding AMSA between 2.1 and 16.4 mVHz (9.4+4.2 mVHz). AMSAmeasured in the circulatory phase (N=19) was significantly higher thanthat in the metabolic phase (N=22) (8.14+3.17 vs. 5.98+2.88, p=0.03).Linear regression revealed that AMSA decreased in the analyzedpopulation by 0.22 mVHz for every min of VF. AMSA was able to predictcirculatory phase with an accuracy of 0.7 in ROC area. An AMSA thresholdof 10 mVHz was able to predict the circulatory phase with sensitivity of30%, specificity of 95%, PPV of 86%, NPV of 62%, and overall accuracy of66%.

FIG. 1D is a table 100D showing examples that relate AMSA to predictedlikelihood of failure in defibrillating a victim who has or has not beenpreviously defibrillated. The data was generally analyzed to determinethe correlation between AMSA values and prior defibrillation success orfailure with respect to success of subsequent defibrillation attempts.

The table shows the results of analysis of 1291 quality defibrillationevents from 609 patients. AMSA was calculated for each such set of databased on a 1024 point ECG window that ended 0.5 seconds before eachdefibrillation. In the data, defibrillation was deemed successful when aspontaneous rhythm existed equal to or greater than 40 bpm and startingwithin 60 seconds from the shock, and also lasting for more than 32seconds. A range of AMSA thresholds was calculated and evaluated for thedata. The actual results shown in the other tables use the same orsimilar data.

In summary of the data, where no prior defibrillation had occurred, themean AMSA for successful shocks was 16.8 mVHz, while the mean forunsuccessful shocks was 11.4 (p<0.0001). For subsequent shocks, the meanAMSA value fell to 15.0 for successful shocks and 7.4 for unsuccessfulshocks.

Referring more specifically to the table itself, examples of data fromdefibrillation events were binned according to different AMSA valuesapplied to the data as AMSA thresholds that would be used to determinewhether to apply a subsequent shock. The first column of the table showsthe different assigned AMSA values, while the second column shows thenumber of events that the particular chosen AMSA value correctlypredicted, as compared to data indicating whether a defibrillation thatwas then applied was successful. The last column shows percentages withwhich the relevant AMSA value would have resulted in an accurateprediction if it had been used in the situations represented by the testdata.

The upper section shows statistics for a first defibrillation attemptfor each patient, while the lower section shows data for subsequentdefibrillation attempts. The data indicates that lower AMSA values canprovide more accurate predictions for subsequent defibrillations thanfor earlier defibrillations.

The upper portion of the table shows a comparison of aggregate mean AMSAvalues of first versus second shock, second versus third shock, etc. Asthe data indicates, such AMSA values generally decrease from the firstdefibrillation attempt to the second, and to a lesser amount generallyfor each additional defibrillation attempt.

FIG. 1E is a schematic diagram 100E of a data structure for correlatingAMSA and prior defibrillation shocks to predicted outcomes for shockinga victim. The data structure here is greatly simplified in an effort toshow how AMSA values and determinations about a number of prior shocks(successful or unsuccessful) can be used to predict whether anothershock can succeed. This particular table shows correlations for priorshocks generally, though additional tables can be used for identifyingcorrelation for prior successful or unsuccessful shocks.

The table is shown in a format, by which a program or human user couldenter at one side of the table to select the value of one inputvariable, and then move across to the value of another variable, andobtain for an output a percentage likelihood of success, For example,the number of prior shocks are listed across the x-axis at the top ofthe table, while the percentage likelihood of success is shown along theright edge on the y-axis. The values in the body of the table are AMSAvalues that have been normalized to a 0 to 100 scale. The actual valuesare not intended to represent any actual outcome or actual numbers, butsimply to indicate the interaction of the various values in coming to aconclusion about a likelihood of success.

Thus, for example, if a patient has received two defibrillating shocks,one would move to the third column of the table and then move down to ameasured AMSA number—say 60. One would then move to the right edge tosee the percentage likelihood of success—here, 70%. Values between thoseshown in the cells of the table can be rounded or interpolated orotherwise handled so as to provide likelihoods between each 10% valueshown in the data structure.

The likelihood of success identified from the data structure can then beused in various ways to implement the likelihood determination, such asproviding the number for the determined likelihood to a microprocessorthat can use it to determine whether to enable the shocking capabilityof a defibrillator and/or to display the value or a related value on thedefibrillator for review by a rescuer. Where additional factors (e.g.,trans-thoracic impedance) are to be considered, the table can take onadditional dimensions, multiple tables can be used, or other techniquesfor generating a likelihood that is a composite of multiple differentfactors can be used.

FIG. 1F is a table 100F showing predictions of successful defibrillationfor different AMSA threshold values for instances of firstdefibrillation attempts. The threshold values are listed in the firstcolumn, and the cells to the right of each AMSA value indicateparticular outcomes for shocks delivered at those AMSA values forinitial shocks.

The particular values shown include sensitivity, specificity, positivepredictive value (PPV), negative predictive value (NPV), and accuracy,which are statistical measures of the performance of AMSA prediction forshock outcome. Sensitivity indicates the proportion of actual shocksuccesses that were correctly identified. For example, if there were 100shock successes, and 60 of the 100 were identified by an AMSA thresholdof 10 mVHz, then the sensitivity is 0.6 using 10 mVHz as the AMSAthreshold. Specificity represents the proportion of shock failures thatwere correctly identified by the particular AMSA value. PPV is the shocksuccess rate. For example, if 10 mVHz was used as the AMSA threshold todeliver shocks and 100 shocks were delivered with 60 defibrillationsuccesses, PPV=0.6. NPV is the shock failure rate. For example, if 10mVHz was used as the AMSA threshold for the 100 cases, with AMSA<10failing to shock, there are 90 cases of failed shock, or NPV=0.9.Accuracy is the proportion of true results (correctly predicted as shocksuccess and shock failure by AMSA) in the total patient population.

FIG. 1G is a table 100G showing AMSA prior defibrillation for refractoryand recurrent VF. In particular, the table shows AMSA values that weremeasured before a defibrillating shock was delivered, and thencorrelated to whether the shock was successful or not. The first rowshows the mean AMSA for all shocks, successful or unsuccessful, brokenout by whether refractory VF was present or recurrent VF was present(where mean+/−SEM is shown for each of the values in the table). Thesecond row shows the AMSA, for both refractory and recurrent VF, wherethe result of the shock was a successful defibrillation, while the thirdrow shows corresponding values for shocks that did not successfullydefibrillate. The final row shows the shocks that were successful indefibrillating the subject, both in terms of percentage and numbers. Ascan be seen, the level of success was much higher for recurrent VF thanfor refractory VF, and the AMSA was also higher.

FIG. 1H is a table 100H showing prediction of successful defibrillationfor increasing AMSA threshold values in the instances of refractory VF.The parameters shown in the table are similar to those shown for FIG.1E.

FIG. 1I shows examples of window functions 100I and resulting FFTs fromthose functions. As noted above, window widths in the time domain ofless than 4 second down to about one second, less than three secondsdown to about one second, and less than two seconds down to about onesecond, can be used. The figure shows, at the top, a boxcar window thatis not tapered and thus can have negative transitory effects introducedinto the FFT that it produces. The figure shows, at the bottom, a Tukeywindow, which is tapered as a sine wave, and is capped at a maximumvalue before coming down on the back side according to the decreasingvalue for the sine wave. The window thus lessens the effect oftransients cause by the sudden switching of the boxcar window.

FIG. 1J shows a diagram 100J including ROC (receiver operatingcharacteristic) Area values for five different window functions appliedto a one second window of ECG data. In this example, digitalized ECGrecordings were collected from multiple emergency medical services inthe U.S. through a regular field case submission program. The samplingrate of all the ECG data files was 250 Hz. An episode of 1.025 seconds(256 data points, sample rate 250 Hz) waveform ending at 0.5 secondsbefore each shock attempt were selected for analysis. Five windowingfunctions were used for analysis. Shock success was defined as anorganized rhythm that was present for a minimum of 32 seconds, startingwithin 60 seconds after the shock, and that had a rate of 40 beats perminute or greater.

Some values shown in the figure have diagnostic value when used incombination with the methods discussed here. For example, when comparingone method of analysis to another, a “p-value” provides a measure of adifference between two groups of measurements, with lower p-valuesgenerally being better compared to higher p-values. By statisticalconvention, a value of p<0.05 is considered to be statisticallysignificant. An Area under the Curve (“AUC”) measures the area under theROC curve. The “squarer” the ROC curve is, the greater the accuracy ofthe diagnostic in general; the AUC is greater for “squarer” curves. TheChi-square test is a simple statistical comparison of the probabilitydistribution of two or more groups where the outcomes are binary.

A total of 1291 shocks (321 successful) from 609 patients with witnessedVF were included in the analysis. As shown in FIG. 1J, a Tukey window(R=0.2) resulted in significantly higher area under the ROC curvecompared to other FFT windows.

Thus, as shown by this study, a defibrillator or other device asdiscussed above and below can be programmed to make AMSA determinationsfor purposes of predicting a likelihood of successful defibrillatingshock using a Tukey window of a width of about 1 second. In otherinstances, it can be determined that one of the other three types oftapered windows is appropriate, or at least more appropriate than thenon-tapered rectangular, or boxcar, window function. Similarly, multipledifferent window functions can be used for a particular patient, and anAMSA value can be generated from a combination of the different windowfunction readings.

Each of these tables represent values that can be provided as parametersfor the operation of a device that determines likelihood of success fora shock or provides other determinations for use in providing care to apatient suffering from VF. For example, the values determined fromtesting a large number of past events can be used as values thatdetermine the likelihood values that a device correlates with aparticular AMSA value at a particular time after VF starts. In thismanner, then, data from observations of care provided to prior patientscan be used to program a system for providing better case to futurepatients, particularly with respect to providing guidance on when ashock is likely to be successful in defibrillating the patient.

Referring to FIG. 1L, a chart 100L tabulates AMSA data from aninvestigation in which CPR was simulated by using extracorporealcirculation (ECC) on open-chest swine. During the investigation, VF wasinduced and each (of eight) swine were left untreated for eight minutes.After this eight-minute time period, the ECC was initiated andmaintained for a ten minute period while the flow was adjusted toproduce a coronary perfusion pressure (CPP) of 10 mmHg. After deliveryof an initial defibrillation shock, the ECC flow was increased andtitrated to secure a mean aortic pressure of 40 mmHg and additionalelectrical shocks were delivered at 60 second intervals. In this model,defibrillator shock success was defined as organized rhythm lasting morethan 5 seconds. As represented in the chart, blood flow in the leftanterior descending (LAD) coronary artery relative to baseline LAD bloodflow was determined and represented as a quantity (identified as“LADrf”). Absent intervention, AMSA values generally decline in aprogressive manner over time during VF. From collected data, based uponthe completion of the ECC and prior to applying defibrillation shocks,the animals were assigned to one of two groups. In one group(represented in the chart of FIG. 1L as “Grp 1” and of which fouranimals were assigned), there was no change or a decrease in AMSA values(i.e., change in mean value being −1.1±1.2) over the time period of thestart of ECC to end of ECC. For the second group (represented in FIG. 1Las “Grp 2”), which contained the remaining four animals, the datareported an increase in AMSA values (i.e., change in mean being+3.7±2.7)with all animals showing a progressive increase in AMSA over the periodof start of ECC to end of ECC. Regarding the LADrf flow just prior tofirst shock being administered, the flow trended higher for the Group 2animals, compared to the Group 1 animals. As such, the AMSA values andthe LADrf flow quantities collected from the Group 2 animals have largerand thereby better levels than the corresponding quantities of the Group1 animals. The chart also reports, for each group, the period of time toa successful defibrillation shock. In particular, in Group 2 animals asuccessful first shock was achieved in less time than in Group 1 animals(e.g., approximately 721 seconds for Group 2 versus 837 seconds forGroup 1).

Based upon these quantities, in particular the AMSA values, the Group 2animals have a better predicted likelihood of shock success compared tothe Group 1 animals, which generally to achieve a successful first shockafter a longer period of time. As such, from the chart data, AMSA values(calculated prior to defibrillation), temporal trends in the data, etc.can be used for treatment determinations. For example, for relativelyflat or decreasing trends in AMSA values, CPR efforts can be recommendeduntil the AMSA values change (e.g., increase, a positive trend ismeasured, etc.). Translated into clinical terms, if CPR is beingperformed on a patient and the AMSA values increase to show a positivetrend, the likelihood of a successful shock can be considered higherthan if it were a trend of little or no change, i.e. insignificantchange, or a decreasing trend. For instance, the series of transformvalues, such as AMSA can be considered to have a trend of insignificantchange (or a decreasing trend) if AMSA increases by less than 10% overthe course of one minute of resuscitation treatment. Statisticalanalyses such as control charts, change point analysis, or other timeseries analyses can be employed to determine whether the series oftransform values changes over a period of time to a threshold degree.Alternatively, the shape of the transform value trend can also beanalyzed to determine if AMSA has stopped increasing, and/or issubstantially flat. In some implementations, at the time when AMSA is ata maximum (or within a predetermined range of the maximum), but beforebeing at the maximum (or within the predetermined range) for more than athreshold amount of time (e.g., 32 seconds), it can be desirable todeliver a shock. In some implementations, it could be desirable todeliver a shock before the transform value starts to decay. This can beindicated, for example, in the shape analysis of the trend as azero-crossing of the first derivative (or the second derivativeexceeding a negative value above a threshold). However, if the AMSAvalues remain relatively flat (or decrease) as CPR is being performed,the rescuer can be recommended to continue chest compressions, toprovide a pharmacologic agent (i.e., epinephrine) to increase centralblood pressures, to change their chest compression technique (e.g.,perform deeper compressions, compressions of faster rate, etc.), or toperform another intervention technique to increase the AMSA values (andcorrespondingly increase the likelihood of a successful shock).

FIG. 1M is an example of a graphical representation 100M that can bedisplayed by a patient monitoring and/or treatment device. The examplegraphical representation 100M includes a parallel display of an ECGsignal 152 a, AMSA 152 b, corresponding to the ECG signal, and a CPRsignal 152 c, recorded in parallel with the ECG signal. Line 152 b isrepresented as AMSA values computed periodically throughout the allottedtime period, including during cardiac treatment (e.g., CPR).

The example graphical representation 100M illustrates AMSA 152 b in apatient suffering of VF, being treated with CPR according to standardprotocol (e.g., completing 2 minutes of CPR between each singledefibrillation attempt). In the illustrated example, two defibrillationshocks were delivered to the patient. The first shock, which failed, wasdelivered at around 10 minutes and the second shock, which succeeded,was delivered at around 13 minutes. The average AMSA value measured overa period of few seconds prior to the first shock (AMSA₁) was about 4.9mVHz, which is below an early shock threshold, such as approximately 12mVHz, approximately 13 mVHz, approximately 14 mVHz, approximately 15mVHz, or another threshold value. The average AMSA value 158 measuredover a period of few seconds prior to the second shock (AMSA₂) was about8.6 mVHz. The general trend of AMSA 152 b over time illustrates agenerally increasing trend between AMSA₁ and AMSA₂, notably during CPRpauses.

In this example, three points on the AMSA line 152 b are particularlyrelevant, corresponding to certain evaluation periods: points 154, 156and 158, which were calculated during CPR pauses to avoid compressionartifacts. These points represent evaluation periods at which thecombined AMSA value measurement (e.g., mean or median value determinedover a window of time) are below a predetermined value associated withdefibrillation success, but the change from the first recorded AMSAvalue AMSA₁ (4.9 mVHz) to each of these three points can be used asindicators of defibrillation success. For example, referring to point156 (taken at a time when there is a pause in CPR compressions, whichcan generally provide for more reliable AMSA values than when CPRcompressions are being administered), the respective AMSA value is about9 mVHz, which corresponds to a change in AMSA of approximately over 4mVHz. Such a change in AMSA is indicative of a relatively highlikelihood of shock success, at least comparable or greater than theAMSA value at point 158. Such data can indicate that analyzing AMSA inparallel with or in between CPR signals can assist a rescuer inproviding successful defibrillation therapy at time intervals differentthan the standard protocol, defining a personalized treatment optimizedfor each patient, which can be materially different for differentpatients. For instance, as shown above, because the change in AMSA fromthe first recorded AMSA value AMSA₁ to point 156 is substantial, thesystem can provide a recommendation and/or decision for the patient tobe treated with an electrical shock at a time (e.g., point 156) prior tothe standard treatment protocol, rather than withholding shock treatmentuntil point 158.

FIG. 1N is another example of a graphical representation 100N that canbe displayed by a patient monitoring and/or treatment device. Theexample graphical representation 100N includes an AMSA trend 162 of apatient receiving cardiac therapy, such as CPR. Line 162 is representedas being drawn through a portion or all of the AMSA values computedperiodically throughout the time of a cardiac treatment (e.g., CPR). Asillustrated, AMSA values fluctuate over time, and such variationrepresents changes in the victim's ECG where the changes can representchanges in likelihood that a shock, currently delivered, can besuccessful. But although there is relatively large variation over shorttime periods, the variation is less over longer time windows, such asover 10 or more seconds.

For example, AMSA values can be computed periodically over a short timeperiod, and more general values can be computed by averaging orotherwise combining the individual measurements. In someimplementations, AMSA can be displayed as a running average. Forexample, line 162 can represent the average of past computations, andcan also be extended into the future in some implementations, such as bylinear regression or other appropriate statistical techniques.

Each of the points included in the AMSA trend 162 (e.g., points 164, 166and 168) can be mapped to the time axis. The first determined AMSA value(e.g., point 164 measured at to) can be above or below a predetermineddefibrillation threshold (e.g., 15 mVHz). Generally, the firstdetermined AMSA value varies between different victims and differentcardiac events, where the changes are driven in large part by ischemiceffects that the event has on the heart tissue.

FIG. 1N further depicts a line 170 that indicates a threshold abovewhich a defibrillating shock is advised. When the AMSA trend 162 exceedsthis threshold, the overall percentage of shock success can berelatively high, in which a shock can be recommended. Though, when theAMSA trend 162 remains below this threshold, the change in AMSA can bemore relevant to determining the overall percentage of shock success.

As noted herein, the actions performed by a medical device, such as adefibrillator, can be guided or triggered by one or more AMSA values.For example, if initial AMSA value is above a predetermineddefibrillation threshold (e.g., 15 mVHz corresponding to 60% probabilityof successful defibrillation) a defibrillation shock can be delivered.In some implementations, a lookup table or graph, such as the shocksuccess rate to AMSA curve illustrated in FIG. 1P can be used todirectly identify the probability of successful defibrillationcorresponding to each measured initial AMSA value. The formula thatdescribes the relationship between the initial AMSA value and theprobability of successful defibrillation, shock successrate=1/(1+(AMSA/Constant)³) can also be used. The constant can beassociated to one or more physical parameters, such as the energy of adefibrillation shock.

In some implementations, experimental values such as the measurementresults 100R illustrated in FIG. 1R can also be used as a guide todirectly identify the probability of successful defibrillationcorresponding to each measured initial AMSA value. The shock of successcan vary as a function of AMSA and other parameters, such as the energyof the defibrillation shock. The medical device can automaticallyprocess the detected AMSA and use one of the described methods ofdetermining shock success or any other methods appropriate fordetermining shock success to provide an indicator to the user of themedical device. The indicator can include a numerical display of theprobability of success, a written recommendation and/or a visual displaybased on the graphs illustrated in FIGS. 1P and 1R.

If AMSA value is below the predetermined defibrillation threshold (e.g.,15 mVHz) AMSA value can be continuously monitored and the change in AMSAbetween times t₁ and t₀ or t₂ and to can be used to determine when andif a defibrillation shock can be delivered. For a majority of patientswith low initial AMSA (as illustrated in FIG. 1M), CPR cannot be able togenerate an increase of AMSA to reach the early shock threshold, such asapproximately 12 mVHz, approximately 13 mVHz, approximately 14 mVHz,approximately 15 mVHz, or another threshold value. In someimplementations, an upward overall trend (e.g., linear, non-linear,average increase over time) in AMSA can be used as an indicator thatdefibrillation can be successful. For example, an absolute change inAMSA determined as the difference between an initial AMSA value 164 anda later AMSA value (e.g., 166 or 168) can be calculated. The change inAMSA value over time can be used in determining a probability ofdefibrillation success. In some implementations, each unit increase inAMSA, can be associated to a particular percentage increase of the oddsof shock success, for example, as illustrated in FIGS. 1Q and 1S. Theupward trend in AMSA (or other frequency-based value, as illustrated inFIG. 1S) over time can be determined over any suitable time period inwhich resuscitation and/or therapeutic activities are occurring. In somecases, the upward trend can occur for a short, fleeting period, leadingto a short interval of opportunity in which the administration of ashock or other appropriate therapy is likely to be successful, despite agenerally downward trend over a longer period. The change in AMSA, and,in particular the identification of an upward trend, can be calculatedor otherwise determined via any suitable mathematical method. Forexample, the change in AMSA can be estimated based on calculating aslope of a line intersecting two or more AMSA points, by using apolynomial function, by implementing a non-linear function, calculatinga spline estimation, by determining the derivative, by using regressionanalysis, by applying interpolation techniques, and/or other methodsfamiliar to those of skill in the art.

In some implementations, a change in AMSA can be a more sensitiveindicator for shock success in patients with low initial AMSA and ametric derived from the change in AMSA can be useful to guide CPRefforts, including timing of shock delivery. In some implementations, atable or an odds ratio-AMSA range curve can be used to directly identifythe increase in defibrillation success for each mVHz change in AMSA, asillustrated in FIGS. 1Q and 1S, respectively.

FIG. 1O is another example of a graphical representation 100O that canbe displayed by a patient monitoring and/or treatment device. Theexample graphical representation 100O includes an AMSA trend 182 of apatient who might not be responding at all times to the received cardiactherapy and a line 190 that indicates a threshold above which adefibrillating shock is advised. Line 182 is represented as being drawnthrough a portion or all of the AMSA values computed periodicallythroughout the time of a cardiac treatment (e.g., CPR). As illustrated,AMSA values fluctuate over time, and such variation represents changesin the victim's ECG where the changes can represent changes inlikelihood that a shock, currently delivered, can be successful.

Each of the points included in the AMSA trend 182 (e.g., points 184, 186and 188) can be mapped to the time axis. First AMSA value (e.g., point184 measured at to) can be above a predetermined defibrillationthreshold (e.g., 15 mVHz) and can quickly (e.g., within seconds) dropunder the predetermined defibrillation threshold. Generally, the firstdetermined AMSA value varies with the time from the onset of the cardiacevent and it can also vary between different victims and differentcardiac events.

As illustrated in FIG. 1O, AMSA values with a generally decreasing trendcan include a temporary increase in AMSA value. For example, a patientcan positively respond to applied CPR therapy, or anothercirculation-inducing therapy, for a limited period of time. Theimprovement in myocardial viability can be reflected by an increase inAMSA. In some patients AMSA value can increase above a predetermineddefibrillation threshold (e.g., 15 mVHz), reaching a value at which ashock can be recommended. Or, for some patients, as illustratively shownin FIG. 1O, AMSA trend 182 can remain below this threshold, yet a changein AMSA (e.g., between AMSA point 186 measured at t₁ and AMSA point 188measured at t₂) recorded during a short time interval can indicate anincrease in the overall percentage of shock success.

In some implementations, an absolute change in AMSA determined as thedifference between an initial AMSA value 184 and a later AMSA value(e.g., 186 or 188) can be calculated. The change in AMSA value over timecan be used in determining a probability of defibrillation success. Insome implementations, each unit increase in AMSA, can be associated to aparticular percentage increase of the odds of shock success. A table oran odds ratio-AMSA range curve can be used to directly identify theincrease in defibrillation success for each mVHz change in AMSA, asillustrated in FIGS. 1Q and 1S, respectively.

FIG. 1Q is a table 100Q showing predictions of successful defibrillationfor different AMSA ranges for instances of first defibrillationattempts, corresponding to each mVHz change in AMSA. The initial AMSAvalues are listed in the first column and the cells to the right of eachAMSA value indicate particular outcomes for shocks delivered at thoseAMSA values for initial shocks. FIG. 1S illustrates an example graph100S depicting predictions of successful defibrillation for differentAMSA ranges for instances of first defibrillation attempts,corresponding to each mVHz change in AMSA. In some implementations, theentire range of initial AMSA values that are lower than 6.5 can beassociated to an odds ratio of 2.675. The initial AMSA values and thechange in AMSA can be used to determine a probability of defibrillationsuccess by using the following formula: shock success rate=odds of shocksuccess/(odds of shock success+1). It can be appreciated that othermethods of determining the odds of shock success, and ultimately thepercentage of shock success, as a function of an initial (or other) AMSAvalue and/or trend of AMSA values can be employed.

As an illustrative example, a patient can present an initial AMSA valueof 8.1 mVHz, which according to the dose-response graph 100P(illustrated in FIG. 1P) corresponds to approximately 20% of shocksuccess rate. As indicated by FIGS. 1Q and 1S, for such a patient, eachunit increase in AMSA corresponds to 20/80=25% increase in odds of shocksuccess. After one minute CPR, if AMSA value steadily increased to 12mVHz (4 units of increase in AMSA), the odds of shock success increasedby 336%, corresponding to 1.04 in odds of shock success. This isequivalent to the probability of shock success, or shock success rate,of 1.04/(1+1.04)=51%, which could be a good indication for an earlydefibrillation. For such patients, even though AMSA value did not reachthe preset threshold of 15 mVHz for the early shock, by using asustained change in AMSA as an indicator, the patient could beidentified as benefiting from an early shock. It should be appreciatedthat the above example is provided for illustratively purposes only andthat other manners of calculation and calibration can be possible. Forexample, as discussed below, it can be possible to provide a robuststatistical regression analysis with appropriate coefficients where themodel takes two inputs of spectral frequency (e.g., AMSA value andchange in AMSA over time, frequency value and change in frequency overtime) and outputs an overall predictor (e.g., percentage) of shocksuccess.

FIG. 1T is an example spectrogram 100T derived from an ECG signalcorresponding to a heart presenting VF. The spectrogram can be used toderive AMSA values or other frequency-based data as a function of timeand/or they can be used to directly derive a metric indicative ofmyocardial viability (e.g., without converting the frequency values toAMSA). The metric can be compared to a predetermined threshold to decidewhether to apply a defibrillation shock or not or it can be used toevaluate a trend in frequency change. The illustrated example presents aVF that is initially treated by extracorporeal circulation, which isstarted at approximately 400 s. The spectrogram indicates a steadyincrease in frequency in response to the induced artificial circulation.In some implementations, an absolute peak value, a change in frequencyor a change rate in frequency can be used to determine a metric thatestimates the probability of successful defibrillation and to provide arecommendation for a defibrillation shock. In the illustrated example,the peak recorded at around 650 seconds and/or the change in frequencybetween 500 seconds and 600 seconds can be used as indicators ofsuccessful defibrillation.

Example B

FIG. 1U illustrates a schematic diagram 100U of a method in an examplethat was used to investigate whether a positive change in AMSA inresponse to CPR would predict resuscitation outcome for return ofspontaneous circulation (ROSC). In this example, the illustrated methodwas applied as a retrospective analysis of out-of-hospital cardiacarrest patients. A single centre database of electrocardiographicdefibrillator records collected from 2007 until 2013 including 248patients with bystander or emergency service (EMS) witnessed cardiacarrest and VF as first recorded rhythm was used for analysis.Accordingly, this study provides a greater level of confidence in theeffectiveness of using an initial frequency-based value (e.g., initialAMSA) and a frequency-based trend (e.g., change in AMSA) as sufficientinputs in determining the probability of success from administering oneor more therapeutic interventions (e.g., defibrillation shock,compressions, ventilation). In this example, a random sample of 82records was extracted and analysed, excluding cases with missing data,no artefact free compression pauses, or less than 60 seconds ofcompressions between first compression pause and first shock. InitialAMSA (AMSA₁ 192) was measured during the first compression pause using a2.1 second window. Post-CPR AMSA (AMSA₂ 194) was measured two secondsafter the last chest compression before the first shock. Change in AMSA(ΔAMSA) was calculated as ΔAMSA=AMSA₂−AMSA₁. Admission to emergencydepartment with ROSC lasting for at least 60 seconds was used as the endpoint. In this example, ER admission was an indicator for shock successfor the patient.

The overall emergency room (ER) admission rate was 78%. The univariablelogistic regression results of all cases are included in table 1.

TABLE 1 ER Admission Odds Ratio 95% CI p AMSA₁ 1.40 112 1.74 0.003 ΔAMSA1.03 0.77 1.40 0.83

The univariable logistic regression results for AMSA₁<7.5 mVHz areincluded in table 2.

TABLE 2 ER Admission Odds Ratio 95% CI p ΔAMSA 1.78 0.98 3.22 0.059

The multivariable logistic regression results of all cases are includedin table 3.

TABLE 3 ER Admission Odds Ratio 95% CI p AMSA₁ 159 1.21 2.09 0.001 ΔAMSA155 1.002 2.41 0.049

Multivariable logistic regression showed that both AMSA₁ and ΔAMSA wereindependent predictors of ER admission with odds ratios of 1.59 (95%confidence interval CI 1.21-2.09, p<0.001) and 1.55 (95% confidenceinterval 1.002-2.41, p<0.049) for each mVHz increase in initial AMSA orΔAMSA, respectively.

In analysed VF patients, a high initial AMSA value predicted anincreased likelihood of ER admission (i.e., shock success). An increaseof AMSA in response to CPR also predicted a higher ER admission rate.Monitoring of AMSA during resuscitation therefore may be useful to guideCPR efforts, possibly including timing of shock delivery. The findingssupport the value of AMSA and/or other frequency-based calculations asindicator of myocardial viability and predictor of therapeutic success.

Referring now to FIG. 2, a schematic block diagram 200 shows an exampledefibrillator 201, along with the example electrode package 102 andcompression puck 104, of FIG. 1A in more detail. In general, thedefibrillator 201, and optionally one or more of the electrode package102 and compression puck 104, defines an apparatus for administeringcare to a patient, subject, or individual (e.g., victim 122) whorequires cardiac assistance.

The defibrillator 201 includes a switch 202 and at least one capacitor204 for selectively supplying or applying a shock to a subject. Thedefibrillator 201 further includes an ECG analyzer module 206, atrans-thoracic impedance module 208, a CPR feedback module 210 thatcontrols frequency and magnitude of chest compressions applied to asubject, a patient treatment (PT) module 212 (which includes adefibrillation history analyzer 215), a speaker 214, and a display 216.In this example, the ECG analyzer module 206, trans-thoracic impedancemodule 208, CPR feedback module 210, and patient treatment (PT) module212 are grouped together as a logical module 218, which can beimplemented by one or more computer processors. For example, respectiveelements of the logical module 218 can be implemented as: (i) a sequenceof computer implemented instructions executing on at least one computerprocessor of the defibrillator 201; and (ii) interconnected logic orhardware modules within the defibrillator 201, as described in furtherdetail below in connection with FIG. 9.

Similar to using individual AMSA values, multiple AMSA values can beused for making treatment determinations. For example, time series dataof AMSA values, discernible trends of AMSA values, etc. can be used todefine one or more conditions for which particular treatments, treatmentadjustments, etc. should be employed. For example, AMSA time series datacan be used for predicting the likelihood of successful defibrillation,indicating effective CPR, etc.

Similar to using AMSA values for estimating likelihood of defibrillationsuccess, quantities calculated from AMSA values can be used fortreatment determinations. Trending of AMSA values can be quantified(e.g., by differentiating portions of AMSA value time series), data canbe normalized, weighting can be applied, various operations applied tothe AMSA values, etc. to determine the likelihood of success or otherquantities. In analyzing trends of AMSA values, the actual AMSA values(e.g., initial value) can factor in treatment determinations. Forexample, an AMSA value of 15.0 can be considered appropriate (e.g.,large enough) to indicate a good likelihood of defibrillation success.Correspondingly, values near 15.0 can also be considered a goodindication of a likelihood of defibrillation success. So even if a flattrend or a minimal positive trend is detected (e.g., AMSA values overtime remain constant at 15.0 or only slightly increase to 16.0), theactual AMSA value (e.g., 15.0 or slightly larger) can govern and a goodlikelihood of a successful shock can be reported by the defibrillator.Alternatively for lower AMSA values, data trending can be heavilyweighted. For example, due to CPR being applied a patient's AMSA valuecan significantly change from 5.0 to 12.0. Based upon such a positivetrend in the AMSA values, a determination can report that the likelihoodof shock success has increased and defibrillation can be administered.

To present the AMSA values, trend data, etc. (e.g., represented in thechart) to a rescuer or other individual, one or more techniques can beutilized. A graphical display incorporated into a defibrillator (such asthe defibrillators described above and below) can present individualAMSA values, time averaged values, etc. in near real time to provide anumerical quantity of the patient's condition and the likelihood ofdefibrillation success (e.g., a value of “5.0 AMSA” can be considered asa value with a low likelihood of success while a value of “15.0 AMSA”can be considered as representing a relatively high likelihood ofsuccess). Graphical representations can also be employed to present thetrending of the AMSA time series data. Positive trending values can begraphically represented in one color (e.g., blue) while relatively flator negative trending AMSA values can be representing in anothereye-catching color (e.g., red). Provided such image cues, rescuers canquickly determine if CPR efforts should continue (since a highlikelihood of defibrillation success has not been reached), if CPRefforts should be adjusted (e.g., adjust to deeper and fastercompressions based upon negatively trending AMSA values), if CPR can behalted for applying a defibrillation shock, etc. A threshold can be setfor desired improvement in AMSA

Similar to graphical representations, other types of representations(e.g., audio alerts, guidance messages, etc.) can be employed by adefibrillator (or other type of computing device) to indicate whetherchest compressions are occurring (e.g., by using an accelerometersignal) and generate an output indicating that AMSA value should not becalculated or that the user interface should not provide a value forAMSA on the display, e.g., because the chest compressions may introduceartifacts into the calculation of AMSA values that interfere incalculating an accurate AMSA value. Accordingly, when chest compressionsare occurring, the system may be configured not to display the currentvalue of AMSA (e.g., due to signal artifacts), and when chestcompressions are not detected, the system may then continuouslycalculate and display the current value of AMSA for the user to make adecision of what type of interventional therapy to provide (e.g., chestcompressions, ventilations or defibrillation shock)

Similar to determining the likelihood of defibrillation success, AMSAvalues can be used to make other determinations such as classifyingcardiac rhythm in VF or in asystole, a state of no cardiac electricalactivity, as well as identifying treatments for patients classified inVF or in asystole. For example, based upon a threshold defined by anAMSA value, a patient can be identified as being in VF or in a state ofno cardiac electrical activity referred to as asystole (colloquiallyknown as flat line). Generally, CPR should be employed (or continued) ifa patient is asystolic since shock treatment cannot improve thepatient's condition and in some situations can worsen their condition.One study has demonstrated that asystole following defibrillation canproduce a worse prognosis than primary asystole or pulseless electricalactivity (PEA). By investigating the relationship between pre-shock AMSAvalues and the appearance of post-shock asystole, one or moredetermination techniques can be identified for either applying a shockor initiating (or continuing) a non-shock treatment such asadministering CPR.

In one investigation, ECG recordings, sampled at 250 Hz, were digitizedand data associated with initial shocks at a particular energy level(i.e., 120 Joules) was reviewed. Episodes of approximately two seconds(e.g., 2.05 seconds or 512 data points) that terminated a half secondbefore a shock attempt were analyzed for AMSA values. As illustrated bya chart 100K shown in FIG. 1K, post shock rhythms were annotated as VF,asystole, PEA or tROSC (i.e., an organized rhythm present for a minimumof 32 seconds, started within 60 seconds after that shock, and having arate of 40 beats per minute or larger). Data from a total of 543patients with VF was investigated. From the data, for AMSA values of 3mVHz or less, defibrillation resulted in 77.8% post-shock asystole and22.2% of other non-perfusing rhythms (with no instances of tROSC). Asillustrated in the figure, for AMSA values larger than 3.0 mVHz,asystole levels reported considerable decreases along with correspondingincreases in post-shock VF, PEA and tROSC.

One or more conditions can be predefined for determining whether adefibrillation shock should be initiated for treatment. For example, aninitial AMSA value can be determined from a patient's ECG, and then themeasured AMSA value can be compared to a threshold value (e.g., an AMSAvalue of 3 mVHz). For measured values equivalent to or exceeding thethreshold, defibrillation treatment can be deemed appropriate andinitiated. For measured values below the threshold (e.g., below 3 mVHz),asystole (e.g., as predominate post-shock rhythm) can be consideredprobable and rhythm restoration by defibrillation can prove to befutile. As such, another recommended treatment such as CPR would beinitiated or continued (if previously initiated).

Such determinations can be executed by one or multiple systemcomponents, for example, the AMSA analyzer 108 (shown in FIG. 1A) canutilize data from the ECG unit 106 (which can be part of a portabledefibrillator) to determine if a predefined threshold (e.g., an AMSAvalue of 3 mVHz) has been met or exceeded. System equipment, modules,etc. described above and below can assist in determining and utilizingthis information; for example, equipment can be used to deliver adefibrillating shock to a patient if a determined AMSA value (measurefrom the patient's ECG data) exceeds the predefined AMSA threshold.Along with different AMSA values (e.g., larger or smaller than 3 mVHz)being used for such determinations, other processing techniques can beemployed. For example, multiple values (e.g., current and previous AMSAvalues) can be employed such that historical trends (hysteresis) factorinto VF determinations and whether to use defibrillation or continueCPR.

In the example of FIG. 2, the electrode package 102 is connected to theswitch 202 via port on the defibrillator 201 so that different packagescan be connected at different times. The electrode package 102 can alsobe connected through the port to ECG analyzer module 206, andtrans-thoracic impedance module 208.

The compression puck 104 is connected, in this example, to the CPRfeedback module 210. In one embodiment, the ECG analyzer module 206 is acomponent that receives an ECG (e.g., ECG signal 132). Similarly, thetrans-thoracic impedance module 208 is a component that receivestransthoracic impedance (e.g., trans-thoracic impedance signal 110).Other embodiments are also possible.

The patient treatment module 212 is configured to receive an input fromeach one of the ECG analyzer module 206, trans-thoracic impedance module208, and CPR feedback module 210. The patient treatment module 212 usesinputs as received from at least the ECG analyzer module 206 andtrans-thoracic impedance module 208 to predict whether a defibrillationevent can likely terminate an arrhythmic episode. For example, ECG datacan be used both to determine AMSA values for a patient, and alsodetermine whether shocks are effective or not so that such informationcan be saved and used to identify likelihoods that subsequent shocks canbe effective). In this manner, the patient treatment module 212 usesinformation derived from both an ECG signal (both for AMSA and foradjusting the AMSA value) and transthoracic impedance measurement toprovide a determination of a likelihood of success for delivering adefibrillating shock to a subject.

The patient treatment module 212 is further configured to provide aninput to each one of the speaker 214, display 216, and switch 202. Ingeneral, input provided to the speaker 214 and a display 216 correspondsto either a success indication or a failure indication regarding thelikelihood of success for delivering a shock to the subject. In oneembodiment, the difference between a success indication and a failureindication is binary and based on a threshold. For example, a successindication can be relayed to the display 216 when the chancescorresponding to a successful defibrillation event is greater than 75%.In this example, the value “75%” can be rendered on the display 216indicating a positive likelihood of success. When a positive likelihoodof success is indicated, the patient treatment module 212 enables theswitch 202 such that a shock can be delivered to a subject.

The patient treatment module 212 can also implement an ECG analyzer forgenerating an indication of heart rate for the patent, for generating anindication of heart rate variability for the patent, an indication ofECG amplitude for the patent, and/or an indication of a first or secondderivative of ECG amplitude for the patient. The indication of ECGamplitude can include an RMS measurement, measured peak-to-peak,peak-to-trough, or an average of peak-to-peak or peak-to-trough over aspecified interval. Such indications obtained by the ECG analyzer can beprovided to compute an AMSA value for the patient and/or can be used incombination with a computed AMSA value so as to generate some derivativeindication regarding whether a subsequent shock is likely or unlikely tobe effective (and the degree, e.g., along a percentage scale, of thelikelihood).

In another embodiment, likelihood of a successful defibrillation eventcan be classified into one of many possible groups such as, for example,low, medium, and high likelihood of success. With a “low” likelihood ofsuccess (e.g., corresponding to a successful defibrillation event isless than 50%), the patient treatment module 212 disables the switch 202such that a shock cannot be delivered to a subject. With a “medium”likelihood of success (e.g., corresponding to a successfuldefibrillation event is greater than 50% but less than 75%), the patienttreatment module 212 enables the switch 202 such that a shock can bedelivered to a subject, but also renders a warning on the display 216that the likelihood of success is questionable. With a “high” likelihoodof success (e.g., corresponding to a successful defibrillation event isgreater than or equal to 75%), the patient treatment module 212 enablesthe switch 202 such that a shock can be delivered to a subject, and alsorenders a cue on the display 216 indicating that the likelihood ofsuccess is very good. Still other embodiments are possible.

Thus, the system 200 can provide, in a portable electric device (e.g., abattery-operated device) the capability to analyze a number of inputsand to identify a variety of factors from those inputs, where thefactors can then be combined to provide a flexible, intelligentdetermination of likely success.

Referring to FIG. 3A an example flow chart of a process 300 foradministering care to a patient requiring cardiac assistance isillustrated. In implementations, the method 300 is implemented by theexample defibrillators described herein, for example, in connection withFIGS. 1B and 2. However, other embodiments are possible.

At a step 302, an ECG signal (e.g., ECG signal 132) is monitored. Ingeneral, an individual receiving cardiac care includes the patient atany time during a cardiac event, including whether or not patient isreceiving active care (e.g., chest compressions).

At a step 304, an optional filter can be applied. For example, ahigh-pass filter with a desired cutoff frequency (preferably but notlimited to be 0.5 Hz) can be applied to remove the baseline drift. At astep 306, a Fast Fourier transform (FFT) is applied to the filtered ECGsignal to generate frequency-domain data. The spectral shape can bequantified using a preferred method and a first frequency-domain valuecan be generated.

At a step 308, a first frequency-domain value is compared to athreshold. In some implementations, the frequency-domain value isdirectly compared to a predetermined frequency-domain threshold or afrequency-domain value can be converted to a probability ofdefibrillation success, which is compared to a predetermineddefibrillation success threshold. If the first frequency-domain valueexceeds the predetermined frequency-domain threshold or if theassociated probability of success exceeds the predetermineddefibrillation success threshold, the process can continue with step 318to indicate a treatment (e.g., defibrillating shock and/or othertherapeutic intervention). If the first frequency-domain value is belowthe predetermined frequency-domain threshold, the process continues tostep 310.

At step 310, a frequency-domain value is continuously monitored over afirst evaluation time period. In some implementations, the firstevaluation time period can correspond to a pause in chest compressionsand/or can be a preset time period (e.g., 1 minute). At step 312, asecond frequency-domain value corresponding to a change infrequency-domain can be determined. In some implementations, the processincludes an automatic identification of a steady change infrequency-domain value using a statistical analysis of thefrequency-domain values recorded during the first evaluation timeperiod. In some implementations, the change in frequency-domain can beprovided as a difference between two frequency-domain values determinedduring the first evaluation time period. It can be appreciated that thechange in frequency-domain can be determined via any suitable methodfamiliar to those of skill in the art. Such values can be determined atany given point (e.g., beginning, middle, or end) of the firstevaluation time period. In some implementations, the change infrequency-domain can be defined as a frequency-domain change rate (e.g.,difference between two frequency-domain values relative to the firstevaluation time period). The two frequency-domain values used todetermine frequency-domain change can be absolute, mean or medianfrequency-domain values. One of the two frequency-domain values can befirst frequency-domain value determined at step 306 or a differentfrequency-domain value determined at a time later than the first time,which corresponds to the beginning of the first evaluation time period.

In some implementations, the frequency-domain data can be subject to aregression analysis. For example, such a regression analysis can involvea statistical model that inputs a first frequency-based value (e.g.,AMSA) based on a time-frequency transformation taken over a firstevaluation period, and further inputs a second frequency-based value(e.g., overall change in AMSA) that represents a trend based on one ormore additional time-frequency transformations taken over a secondevaluation period. The first evaluation period can be a period aroundthe initiation of ECG recording (e.g., including initial AMSA) and thesecond evaluation period can be any time interval subsequent to thefirst evaluation period, expanding over a duration of few seconds. Thesecond evaluation period can also be continuously updated, to follow areal-time recording of the ECG (e.g., including the most recentlyacquired and determined data). The output of the regression analysis canbe a probability of therapeutic (e.g., defibrillation or otherinterventional therapy) success. Regression analysis can be used todetermine weights that produce improved correlation between the weightedsum and the probability of successful defibrillation (or between theweighted sum and the presence of a physiological condition). In variousembodiments, the model for simple linear regression is:

Y=a+b*X

where Y is the dependent variable, X is the independent variable, and aand b are the regression parameters (the intercept and the slope of theline of best fit).

As noted herein, various forms of statistical estimation in accordancewith the present disclosure can take at least two inputs for astatistical model, a frequency-based parameter and a trend of thefrequency-based parameter, where the output of the statistical model isa probability of therapeutic success. An example of a suitablestatistical model that can be used with embodiments described herein isa multiple linear regression, as generally described below.

The model for multiple linear regression is:

Y=a+b ₁ *X ₁ +b ₂ *X ₂ + . . . +b _(i) *X _(i)

The coefficients, b_(i), for each input variable, X_(i), are calculatedusing statistical methods such as the general linear model to provide abest estimate of the probability of defibrillation success, Y. Thevariable, Y, can also represent the probability of success of anytherapeutic intervention other than defibrillation, for instance chestcompressions, ventilations or a metabolic treatment such as epinephrineor aspartate. The variable, Y, can also represent the probability thatthe patient is in a particular physiological state. The general linearmodel (GLM) can estimate and test any univariate or multivariate generallinear model, including those for multiple regression, analysis ofvariance or covariance, and other procedures such as discriminantanalysis and principal components. With the general linear model,randomized block designs, incomplete block designs, fractional factorialdesigns, Latin square designs, split plot designs, crossover designs,nesting, can be explored. The model is:

Y=XB+e,

where Y is a vector or matrix of dependent variables, X is a vector ormatrix of independent variables, B is a vector or matrix of regressioncoefficients, and e is a vector or matrix of random errors.

In multivariate models, Y is a matrix of continuous measures. The Xmatrix can be either continuous or categorical dummy variables,according to the type of model. For discriminant analysis, X is a matrixof dummy variables, as in analysis of variance. For principal componentsanalysis, X is a constant (e.g., a single column of 1s). For canonicalcorrelation, X is usually a matrix of continuous right-hand variables(and Y is the matrix of left-hand variables).

For some multivariate models, it can be easier to use ANOVA, which canhandle models with multiple dependent variables and zero, one, or morecategorical independent variables (that is, only the constant is presentin the former). ANOVA automatically generates interaction terms for thedesign factor.

After the parameters of a model have been estimated, they can be testedby any general linear hypothesis of the following form:

ABC′=D,

where A is a matrix of linear weights on coefficients across theindependent variables (the rows of B), C is a matrix of linear weightson the coefficients across dependent variables (the columns of B), B isthe matrix of regression coefficients or effects, and D is a nullhypothesis matrix (usually a null matrix).

The coefficients, b_(i), are calculated using ECG or other measuredphysiological data collected from a statistically varied population ofsamples to provide a robust database for accurate model generation.Preferably, the resuscitation event is decomposed into multiple therapystates, e.g., arrival at patient's side, pre-shock, post-shock,post-vasopressor, etc., with separate sets of coefficients generated foreach therapy state. The state of therapy, e.g., resuscitation, isdetermined and stored by the defibrillator. For instance when the unitis first turned on and prior to the first shock, the resuscitation isconsidered in the “arrival at patient's side” (APS) state; if CPR isdetected by the defibrillator, it shifts to the “CPR first, no shockstate”; after defibrillation, the state machine shifts to the “firstshock” state. Subsequent shocks cause the state machine to transition tostates for each defibrillation, e.g. “second shock”, etc. Coefficients,b_(i), are calculated for each state and stored on the defibrillator,and used to calculate the most accurate predictor, Y, of therapeuticoutcome (or current physiologic state). Therapeutic outcome, Y, can bescaled so as to provide a value from either zero to one or zero toone-hundred, representing on a scale that is understandable to theoperator that it is a probability; the value of Y can also be unscaled.

Regression can also be performed using the logistic function:

$\mspace{79mu} {\text{?} = {100\left\lbrack {1 - \frac{1}{1 + \text{?} + \text{?}}} \right\rbrack}}$?indicates text missing or illegible when filed

In some examples, such as for a large data set, multivariate logisticregression can be expressed as following:

${\pi (X)} = \frac{^{\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}}}{1 + ^{\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}}}$

The logistic transformation can be derived as following:

$\begin{matrix}{{{\log {it}}\left\lbrack {\pi (X)} \right\rbrack} = {\ln \left\lbrack \frac{\pi (X)}{1 - {\pi (X)}} \right\rbrack}} \\{= {\ln \left\lbrack \frac{\frac{^{\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}}}{1 + ^{\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}}}}{1 - \frac{^{\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}}}{1 + ^{\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}}}} \right\rbrack}} \\{= {\ln \left\lbrack \frac{\frac{^{\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}}}{1 + ^{\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}}}}{\frac{1}{1 + ^{\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}}}} \right\rbrack}} \\{= {\ln \left\lbrack ^{\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}} \right\rbrack}} \\{= {\beta_{0} + {\beta_{1}X_{1}} + {\beta_{2}X_{2}} + \ldots + {\beta_{p}X_{p}}}}\end{matrix}$

Where X₁=AMSA₁ and X₂=ΔAMSA and the coefficients are:

β₀=−5.55612

β₁=0.3742736

β₂=0.6358645

At step 314, a metric of defibrillation success can be determined. Insome implementations, the metric can be determined using the methoddescribed with reference to FIG. 1T. The logistic model is useful inestimating the probability of therapeutic success where the outcome isbinomial and dependent on at least one predictive factor, such thatcertain values of the predictive factor, can be associated withsuccessful defibrillation and other times with unsuccessfuldefibrillations. The logistic curve is a non-linear transformation thatconverts the measured predictive factor into a value approximating aprobability of success. It provides a reasonable, mathematicallytractable approach to minimizing the false negatives and falsepositives.

A threshold can be chosen to optimize both the false negatives (FN) andfalse positives (FP) to provide the best sensitivity and specificity forthe prediction:

Sensitivity=True Positives (TP)/(TP+FN)

Specificity=TN/(TN+FP)

Positive Predictive Value (PPV)=TP/(TP+FP)

Negative Predictive Value (NPV)=TN/(TN+FN)

In some implementations, the metric is provided as a numeric value or aspercentage of probability of defibrillation success. Continuing with theprovided example for large data sets, based on the multivariate logisticregression, the probability of shock success (Pr_(ss)) as a function ofAMSA₁ and ΔAMSA can be determined as:

Pr_(ss)=1/(1+exp(5.55612−0.3742736*AMSA₁−0.6358645*ΔAMSA))).

At step 316, the metric is compared to a second predetermined threshold.If the metric is below the predetermined threshold the process can berepeated from step 312 or 310. If the metric exceeds the predeterminedthreshold, the process 300 can continue with step 318 to indicatetreatment.

In some implementations, the operator can be provided with theprobability of defibrillation success indication or with an indicationof suggested treatment. For example, the operator can be shown apercentage number, or an intuitive display such as a gauge, bar graph,color indication, etc., that indicates a likelihood in percent that theshock can be successful. Alternatively, or in addition, the operator canbe shown a less granular level of an indication, such as a value of“excellent,” “good,” and “poor” to indicate to the operator what thelikelihood of successful defibrillation is. Given this information, theoperator is then faced with a decision of whether to administer one ormore defibrillation shocks.

In some implementations, a trigger mechanism is enabled on thedefibrillator, as discussed above. The trigger mechanism can be enabledwhenever a shockable rhythm is observed for a patient. In othercircumstances, the enabling can occur only when the combined indicationdiscussed above exceeds a threshold value for indicating that a shockcan be successful in defibrillating the patient. For a hybriddefibrillator that is capable of manual and AED modes, the triggermechanism can operate different depending on what mode the defibrillatoris in.

An arrow is shown returning to the top of the process to indicate thatthe process here is in ways continuous and in ways repeated. Inparticular, ECG signals are gathered continuously, as are other types ofdata. And the process repeatedly tries to identify whether a shock canor should be provided, and the order and timing of the steps in thatcycling can be dictated by standards as adjusted by a medical directoror other appropriate individual responsible for the deployeddefibrillator. Thus, for instance, the entire process can be repeated,some portions can be repeated more frequently than others, and someportions can be performed once, while others are repeated.

Referring now to FIG. 3B, another example method 320 is shown foradministering care to a patient requiring cardiac assistance. In someimplementations, the method 320 is implemented by the exampledefibrillators described herein, for example, in connection with FIGS.1B and 2. However, other embodiments are possible.

At a step 322, an ECG signal (e.g., ECG signal 132) is recorded andmonitored. In general, continuous ECG monitoring is standard procedurefor a patient receiving cardiac care, whether or not the patient isreceiving active care (e.g., chest compressions).

At a step 324, a first AMSA value corresponding to a first time point iscalculated from the ECG signal, monitored at step 322. The first AMSAvalue can be determined by integrating the Fourier transform (e.g., FFT)of the ECG signal over a finite frequency range. Example frequencycontent of an arrhythmic ECG signal generally ranges between about 1 Hzto about 40 Hz, with amplitude of about 50 mV or less. An example of anAMSA value calculated from such a signal ranges between about 5 mVHz toabout 20 mVHz.

The AMSA value can be determined from a moving window that moves in timethrough the incoming ECG data as it arrives (e.g., the raw ECG data canbe cached for a period at least as long as the window), where the windowcan be about one second wide (or more), and it can be measured multipletimes each second so that there are overlapping windows. The window canalso have a tapered (rather than rectangular) window function so as toimprove the accuracy of the AMSA value in predicting defibrillationsuccess. The coefficients for the window can be selected to maximize theaccuracy of the calculation. In addition, multiple different AMSA valuescan be determined (e.g., with different window size, type, and/orcoefficients). In some implementations, a single absolute value of themost-accurate AMSA estimate can be provided as output or a compositevalue can be generated from each of the determined AMSA values.

Additionally, the window size, type, and coefficients can change overtime to allow a system to dynamically adjust to a particular VF event.For example, using determinations about the phase in which a VF eventis, a system can change such parameters to switch to a window that isdetermined to better predict defibrillation success. Alternatively, ablend of window techniques can be used and the blend can change overtime, while a composite prediction score is determined from the blendedtechniques.

For example, a system could shift from a symmetric window to anasymmetric window just prior to the end of a CPR interval as it getscloser to the time of a shock. The system can be continuously executinga noise detection process, and if sections of the data in the window arefound to have ECG with anomalously high amounts of higher frequencynoise compared to ECG in adjacent sections, then those portions of thewindow can be attenuated via adjusting the window characteristics. Ifthe burst of noise occurs in the middle of the window, then the windowfunction can be composed of two adjacent Tukey or other windows wherethe null of the superimposed windows is centered at the occurrence ofthe noise burst. Thus, various dynamic changes can be made to the windowas the process occurs so as to adjust to particular activities for apatient.

At a step 326, a first AMSA value is compared to a threshold. In someimplementations, the AMSA value is directly compared to a predeterminedAMSA threshold or the AMSA value can be converted to a probability ofdefibrillation success (e.g., by using the methods described withreference to FIG. 1N), which is compared to a predetermineddefibrillation success threshold. An example predetermined AMSAthreshold can be 12 mVHz and an example probability of defibrillationsuccess threshold can be 50%. If the first AMSA value exceeds thepredetermined AMSA threshold or if the associated probability of successexceeds the predetermined defibrillation success threshold, the processcan continue with step 336 to indicate a treatment (e.g., defibrillatingshock and/or other therapeutic intervention). If the first AMSA value isbelow the predetermined AMSA threshold, the process continues to step328.

At step 328, AMSA value is continuously or intermittently monitored overa first time period (e.g., first evaluation period). In someimplementations, the first time period can correspond to a chestcompression break and/or can be a preset time period (e.g., 1 minute).At step 330, a second AMSA value corresponding to a change in AMSA canbe determined. In some implementations, the process includes anautomatic identification of a steady change in AMSA value (e.g., medianAMSA values are monotonically increasing) using a statistical analysisof the AMSA values recorded during the first time period (e.g., aregression analysis as described with reference to FIG. 3A). In someimplementations, the change in AMSA can be defined as a differencebetween two AMSA values determined during the first time period. In someimplementations, the change in AMSA can be defined as an AMSA changerate (e.g., difference between two AMSA values relative to time). Thetwo AMSA values used to determine AMSA change can be absolute values,mean values or median values extracted from the array of AMSA valuesderived from the frequency domain data or from the output of theregression analysis. One of the two AMSA values can be first AMSA valuedetermined at step 324 or a different AMSA value determined at a timelater than the first time, which can correspond to the beginning of thefirst time period.

At step 332, a metric of defibrillation success can be determined. Themetric can be an indicator of myocardial viability. In someimplementations, the metric can be determined using the method describedwith reference to FIGS. 1Q and 1S. In some implementations, the metricis provided as a numeric value or as percentage of probability ofdefibrillation success. At step 334, the metric is compared to a secondpredetermined threshold. If the metric is below the predeterminedthreshold the process can be repeated from step 322 or 328. If themetric exceeds the predetermined threshold, the process 320 can continuewith step 336 to indicate treatment.

Similar to that discussed above, in some implementations, the operatorcan be provided with the probability of defibrillation successindication or with an indication of suggested treatment. For example,the operator can be shown a percentage number that indicates alikelihood in percent that the shock can be successful. Alternatively,or in addition, the operator can be shown a less granular level of anindication, such as a value of “excellent,” “good,” and “poor” toindicate to the operator what the likelihood of successfuldefibrillation is.

In some implementations, a trigger mechanism is enabled on thedefibrillator, as discussed above. The trigger mechanism can be enabledwhenever a shockable rhythm is observed for a patient. In othercircumstances, the enabling can occur only when the combined indicationdiscussed above exceeds a threshold value for indicating that a shockcan be successful in defibrillating the patient. For a hybriddefibrillator that is capable of manual and AED modes, the triggermechanism can operate different depending on what mode the defibrillatoris in.

An arrow is shown returning to the top of the process to indicate thatat least parts of the process can be continuous performed during cardiacpatient care and at least parts of the process can be repeated. Inparticular, ECG signals are gathered continuously, as are other types ofdata. Process 320 can be implemented as a loop function designed torepeatedly identify whether a shock can or should be provided. The orderand the timing of the steps of the process 320 can be dictated bydifferent medical standards or they can be adjusted by a medicaldirector or other appropriate individual responsible for the deployeddefibrillator. Thus, for instance, the entire process 320 can berepeated, some portions of the process can be repeated more frequentlythan others, and some portions of the process can be performed once,while others are repeated.

FIG. 4A shows a plot of positive predictive value (%) versus AMSAthreshold (mVHz) for a first set of subjects having a trans-thoracicimpedance measured greater than 150 ohms and a second set of subjectshaving a trans-thoracic impedance measured less than 150 ohms. As shownby the comparative data, the first set of subjects generally has agreater positive predictive value for a given AMSA threshold. In bothcases, positive predictive value generally increases with increasingAMSA threshold. Thus, an indication of success for a patient having alow impedance can be provided when the AMSA value is lower, than for acomparable AMSA value from a high impedance patient. Or, where apercentage likelihood of success is shown, the displayed percentage fora particular AMSA value can be higher for a low impedance patient ascompared to a high impedance patient—at least with the range of AMSAvalues from 5-20 mVHz.

FIG. 4B shows a plot of sensitivity (unit-less) versus AMSA threshold(mVHz) for a first set of subjects having a trans-thoracic impedancemeasured less than 100 ohms, a second set of subjects having atrans-thoracic impedance measured between 125 ohms and 150 ohms, and athird set of subjects having a trans-thoracic impedance measured between150 ohms and 180 ohms. As shown by the comparative data, AMSA thresholdgenerally increases, for a given specificity, with increasingtrans-thoracic impedance.

FIG. 5A shows a defibrillator showing examples of information that canbe displayed to a rescuer. In the figure, a defibrillation device 500with a display portion 502 provides information about patient status andCPR administration quality during the use of the defibrillator device.As shown on display 502, during the administration of chestcompressions, the device 500 displays information about the chestcompressions in box 514 on the same display as is displayed a filteredECG waveform 510 and a CO2 waveform 512 (alternatively, an SpO2 waveformcan be displayed).

During chest compressions, the ECG waveform is generated by gatheringECG data points and accelerometer readings, and filtering themotion-induced (e.g., CPR-induced) noise out of the ECG waveform.Measurement of velocity or acceleration of chest compression duringchest compressions can be performed according to the techniques taughtby U.S. Pat. No. 7,220,335, titled “Method and Apparatus for Enhancementof Chest Compressions During Chest Compressions,” the contents of whichare hereby incorporated by reference in their entirety.

Displaying the filtered ECG waveform helps a rescuer reduceinterruptions in CPR because the displayed waveform is easier for therescuer to decipher. If the ECG waveform is not filtered, artifacts frommanual chest compressions can make it difficult to discern the presenceof an organized heart rhythm unless compressions are halted. Filteringout these artifacts can allow rescuers to view the underlying rhythmwithout stopping chest compressions.

The CPR information in box 514 is automatically displayed whencompressions are detected by a defibrillator. The information about thechest compressions that is displayed in box 514 includes rate 518 (e.g.,number of compressions per minute) and depth 516 (e.g., depth ofcompressions in inches or millimeters). The rate and depth ofcompressions can be determined by analyzing accelerometer readings.Displaying the actual rate and depth data (in addition to, or insteadof, an indication of whether the values are within or outside of anacceptable range) can also provide useful feedback to the rescuer. Forexample, if an acceptable range for chest compression depth is 1.5 to 2inches, providing the rescuer with an indication that his/hercompressions are only 0.5 inches can allow the rescuer to determine howto correctly modify his/her administration of the chest compressions(e.g., he or she can know how much to increase effort, and not merelythat effort should be increased some unknown amount).

The information about the chest compressions that is displayed in box514 also includes a perfusion performance indicator (PPI) 520. The PPI520 is a shape (e.g., a diamond) with the amount of fill that is in theshape differing over time to provide feedback about both the rate anddepth of the compressions. When CPR is being performed adequately, forexample, at a rate of about 100 compressions per minute (CPM) with thedepth of each compression greater than 1.5 inches, the entire indicatorcan be filled. As the rate and/or depth decreases below acceptablelimits, the amount of fill lessens. The PPI 520 provides a visualindication of the quality of the CPR such that the rescuer can aim tokeep the PPI 520 completely filled.

As shown in display 500, the filtered ECG waveform 510 is a full-lengthwaveform that fills the entire span of the display device, while thesecond waveform (e.g., the CO2 waveform 512) is a partial-lengthwaveform and fills only a portion of the display. A portion of thedisplay beside the second waveform provides the CPR information in box514. For example, the display splits the horizontal area for the secondwaveform in half, displaying waveform 512 on left, and CPR informationon the right in box 514.

The data displayed to the rescuer can change based on the actions of therescuer. For example, the data displayed can change based on whether therescuer is currently administering CPR chest compressions to thepatient. Additionally, the ECG data displayed to the user can changebased on the detection of CPR chest compressions. For example, anadaptive filter can automatically turn ON or OFF based on detection ofwhether CPR is currently being performed. When the filter is on (duringchest compressions), the filtered ECG data is displayed and when thefilter is off (during periods when chest compressions are not beingadministered), unfiltered ECG data is displayed. An indication ofwhether the filtered or unfiltered ECG data is displayed can be includedwith the waveform.

Also shown on the display is a reminder 521 regarding “release” inperforming chest compression. Specifically, a fatigued rescuer can beginleaning forward on the chest of a victim and not release pressure on thesternum of the victim at the top of each compression. This can reducethe perfusion and circulation accomplished by the chest compressions.The reminder 521 can be displayed when the system recognizes thatrelease is not being achieved (e.g., signals from an accelerometer showan “end” to the compression cycle that is flat and thus indicates thatthe rescuer is staying on the sternum to an unnecessary degree). Such areminder can be coordinated with other feedback as well, and can bepresented in an appropriate manner to get the rescuer's attention. Thevisual indication can be accompanied by additional visual feedback nearthe rescuer's hands, and by a spoken or tonal audible feedback,including a sound that differs sufficiently from other audible feedbackso that the rescuer can understand that release (or more specifically,lack of release) is the target of the feedback.

FIG. 5B shows the same defibrillator, but with an indicator box 522 nowshown across the bottom half of the display and over the top ofinformation that was previously displayed to display a successindication of “75%.” Similar to the display 216 as described above, theindicator box 522 can generally convey a success indication or a failureindication regarding the likelihood of success for delivering a shock toa subject. The success indication can be generated using any combinationof the techniques discussed above, including AMSA values, measures ofprior effectiveness or ineffectiveness of prior defibrillating shocks,and trans-thoracic impedance.

In some implementations, one or more of the inputs used for determininga likelihood that a future shock can be successful, cannot be available.For example, at times it cannot be possible to calculate AMSA accuratelywhen CPR compressions are occurring. Or perhaps a system is receivingvalues for trans-thoracic impedance that are not possible, which wouldindicate a problem with the sensors measuring such impedance or othersimilar problems. In such situations, the score that is generated toindicate a likelihood of success can be switched to a score that dependsonly on n−1 inputs (where n is the optimal number of inputs, and n−1represents the removal of one of the inputs). Thus, the system can beadaptive to problems with particular ones of the inputs that indicate alikelihood of success, yet the system can still determine a likelihoodof success that is as accurate as possible given the inputs that areavailable.

In the example shown, the success indication is textual; however thesuccess indication (and/or failure indication) can generally beimplemented as any type of perceptible feedback. For example, tone,color, and/or other perceptible visual effects can be rendered orotherwise displayed to a user via the indicator box. For example, thecharacters “75%” can be highlighted or otherwise distinguished in a boldcolor, and the phrase “Press to Shock” can blink at least intermittentlyto convey a sense of urgency with respect to a pending shock. Otherembodiments are possible.

FIGS. 6A-6C show example screens that can be displayed to a rescuer on adefibrillator. Each of the displays can be supplemented with anindicator-like box 522 in FIG. 5B when the defibrillator makes adetermination as to the likelihood of success for delivering a shock toa subject.

FIG. 6A shows exemplary information displayed during the administrationof CPR chest compressions, while FIGS. 6B and 6C show exemplaryinformation displayed when CPR chest compressions are not being sensedby the defibrillator. The defibrillator automatically switches theinformation presented based on whether chest compressions are detected.An exemplary modification of the information presented on the displaycan include automatically switching one or more waveforms that thedefibrillator displays. In one example, the type of measurementdisplayed can be modified based on the presence or absence of chestcompressions. For example, CO2 or depth of chest compressions can bedisplayed (e.g., a CO2 waveform 620 is displayed in FIG. 6A) during CPRadministration, and upon detection of the cessation of chestcompressions, the waveform can be switched to display AMSA and a SpO2 orpulse waveform (e.g., a SpO2 waveform 622 is displayed in FIG. 6B).

Another exemplary modification of the information presented on thedisplay can include automatically adding/removing AMSA and CPRinformation from the display upon detection of the presence or absenceof chest compressions. As shown in FIG. 6A, when chest compressions aredetected, a portion 624 of the display includes information about theCPR such as depth 626, rate 628, and PPI 630. As shown in FIG. 6B, whenCPR is halted and the system detects the absence of CPR chestcompressions, the defibrillator can calculate AMSA values 638 and changethe CPR information in the portion 624 of the display, to include anindication 632 that the rescuer should resume CPR, an indication 634 ofthe idle time since chest compressions were last detected and determinedAMSA values 638. In a similar manner, when the defibrillator determinesthat rescuers should change, the label 632 can change to a message suchas “Change Who is Administering CPR.” In other examples, as shown inFIG. 6C, when CPR is halted, the defibrillation device can remove theportion of the display 624 previously showing CPR data and can display afull view of the second waveform. Additionally, information about theidle time 636 can be presented on another portion of the display.

FIGS. 7A and 7B show defibrillator displays that indicate to a rescuerlevels of perfusion being obtained by chest compressions that therescuer is performing. FIG. 7A shows exemplary data displayed during theadministration of CPR chest compressions when the CPR quality is withinacceptable ranges, while FIG. 7B shows modifications to the display whenthe CPR quality is outside of the acceptable range.

In the example shown in FIG. 7B, the rate of chest compressions hasdropped from 154 compressions per minute (FIG. 7A) to 88 compressionsper minute. The defibrillator device determines that the compressionrate of 88 compressions per minute is below the acceptable range ofgreater than 100 compressions per minute. In order to alert the userthat the compression rate has fallen below the acceptable range, thedefibrillator device provides a visual indication 718 to emphasize therate information. In this example, the visual indication 718 is ahighlighting of the rate information. Similar visual indications can beprovided based on depth measurements when the depth of the compressionsis shallower or deeper than an acceptable range of depths. Also, whenthe change in rate or depth indicates that a rescuer is becomingfatigued, the system can display a message to switch who is performingthe chest compressions, and can also emit aural or haptic feedback tothe same effect.

In the examples shown in FIGS. 7A and 7B, a perfusion performanceindicator (PPI) 716 provides additional information about the quality ofchest compressions during CPR. The PPI 716 includes a shape (e.g., adiamond) with the amount of fill in the shape differing based on themeasured rate and depth of the compressions. In FIG. 7A, the depth andrate decrease within the acceptable ranges (e.g., at least 100compressions/minute (CPM) and the depth of each compression is greaterthan 1.5 inches) so the PPI indicator 716 a shows a fully filled shape.In contrast, in FIG. 7B, when the rate has fallen below the acceptablerange, the amount of fill in the indicator 716 b is lessened such thatonly a portion of the indicator is filled. The partially filled PPI 716b provides a visual indication of the quality of the CPR is below anacceptable range.

As noted above with respect to FIG. 5A, in addition to measuringinformation about the rate and depth of CPR chest compressions, in someexamples the defibrillator provides information about whether therescuer is fully releasing his/her hands at the end of a chestcompression. For example, as a rescuer tires, the rescuer can beginleaning on the victim between chest compressions such that the chestcavity is not able to fully expand at the end of a compression. If therescuer does not fully release between chest compressions the quality ofthe CPR can diminish. As such, providing a visual or audio indication tothe user when the user does not fully release can be beneficial. Inaddition, such factors can be included in a determination of whether therescuer's performance has deteriorated to a level that the rescuershould be instructed to permit someone else perform the chestcompressions, and such information can be conveyed in the variousmanners discussed above.

As shown in FIG. 8A, a visual representation of CPR quality can includean indicator of CPR compression depth such as a CPR depth meter 820. TheCPR depth meter 820 can be automatically displayed upon detection of CPRchest compressions.

On the CPR depth meter 820, depth bars 828 visually indicate the depthof the administered CPR compressions relative to a target depth 824. Assuch, the relative location of the depth bars 828 in relation to thetarget depth 824 can serve as a guide to a rescuer for controlling thedepth of CPR compressions. For example, depth bars 828 located in aregion 822 above the target depth bar 824 indicate that the compressionswere shallower than the target depth, and depth bars 828 located in aregion 826 below the target depth bar 824 indicate that the compressionswere deeper than the target depth. Again, then depth is inadequate(along with perhaps other factors) for a sufficient time to indicatethat the rescuer is fatiguing, an indicator to switch rescuers can beprovided in the manners discussed above.

While the example shown in FIG. 8A displayed the target depth 824 as asingle bar, in some additional examples, the target depth can bedisplayed as a range of preferred depths. For example, two bars 829 aand 829 b can be included on the depth meter 820 providing an acceptablerange of compression depths (e.g., as shown in FIG. 8B). Additionally,in some examples, compressions that have depths outside of an acceptablerange can be highlighted in a different color than compressions thathave depths within the acceptable range of compression depths.

The depth bars 828 displayed on the CPR depth meter 820 can representthe compression depths of the most recent CPR compressions administeredby the rescuer. For example, the CPR depth meter 820 can display depthbars 828 for the most recent 10-20 CPR compressions (e.g., the mostrecent 10 CPR compressions, the most recent 15 compressions, the mostrecent 20 CPR compressions). In another example, CPR depth meter 820 candisplay depth bars 828 for CPR compressions administered during aparticular time interval (e.g., the previous 10 seconds, the previous 20seconds).

In some additional embodiments, physiological information (e.g.,physiological information such as end-tidal CO2 information, arterialpressure information, volumetric CO2, pulse oximetry (presence ofamplitude of waveform possibly), and carotid blood flow (measured byDoppler) can be used to provide feedback on the effectiveness of the CPRdelivered at a particular target depth. Based on the physiologicalinformation, the system can automatically determine a target CPRcompression depth (e.g., calculate or look-up a new CPR compressiontarget depth) and provide feedback to a rescuer to increase or decreasethe depth of the CPR compressions. Thus, the system can provide bothfeedback related to how consistently a rescuer is administering CPRcompressions at a target depth, and feedback related to whether thetarget depth should be adjusted based on measured physiologicalparameters. If the rescuers does not respond to such feedback andcontinues performed sub-optimal CPR, the system can then display anadditional message to switch out the person performing CPR chestcompressions.

In some examples, the system regularly monitors and adjusts the targetCPR compression depth. In order to determine a desirable target depth,the system makes minor adjustments to the target CPR compression depthand observes how the change in compression depth affects the observedphysiological parameters before determining whether to make furtheradjustments to the target compression depth. More particularly, thesystem can determine an adjustment in the target compression depth thatis a fraction of an inch and prompt the rescuer to increase or decreasethe compression depth by the determined amount. For example, the systemcan adjust the target compression depth by 0.1-0.25 inches (e.g., 0.1inches to 0.15 inches, 0.15 to 0.25 inches, about 0.2 inches) andprovide feedback to the rescuer about the observed compression depthbased on the adjusted target compression depth. Then, over a set periodof time, the system can observe the physiological parameters and, basedon trends in the physiological parameters without making furtheradjustments to the target compression depth and at the end of the settime period, can determine whether to make further adjustments to thetarget compression depth.

And again, the actual performance of the rescuer against the revisedtarget can be continually monitored to determine when the rescuer'sperformance has fallen below an acceptable level, so that the rescuerand perhaps others can be notified to change who is performing the chestcompressions. Also, each of the relevant parameters of patient conditiondiscussed above with respect to the various screenshots can be made oneof multiple inputs to a process for determining when rescuers who areperforming one component of a rescue technique should be switched outwith another rescuer, such as for reasons of apparent fatigue on thepart of the first rescuer.

The particular devices and displays shown in FIGS. 5A-8B can beimplemented, as noted above, with a system that uses particulartechniques to improve the accuracy of a prediction that an applied shockcan be a success and that uses AMSA or other SPA values in making such aprediction. For instance, the feedback provided by the displays in thefigures can be determined by selecting an appropriate ECG window sizefor calculating AMSA (e.g., one second or slightly longer, such as 1.5seconds or 2 seconds), a window type (e.g., Tukey), and particularcoefficients for the window. Such factors can also be changed over thetime of a VF event, as discussed above, so as to maintain a mostaccurate predictor of defibrillation success.

While at least some of the embodiments described above describetechniques and displays used during manual human-delivered chestcompressions, similar techniques and displays can be used with automatedchest compression devices such as the AUTOPULSE device manufactured byZOLL Medical Corporation of Chelmsford, Mass.

The particular techniques described here can be assisted by the use of acomputer-implemented medical device, such as a defibrillator thatincludes computing capability. Such defibrillator or other device isshown in FIG. 9, and can communicate with and/or incorporate a computersystem 900 in performing the operations discussed above, includingoperations for computing the quality of one or more components of CPRprovided to a victim and generating feedback to rescuers, includingfeedback to change rescuers who are performing particular components ofthe CPR. The system 900 can be implemented in various forms of digitalcomputers, including computerized defibrillators laptops, personaldigital assistants, tablets, and other appropriate computers.Additionally the system can include portable storage media, such as,Universal Serial Bus (USB) flash drives. For example, the USB flashdrives can store operating systems and other applications. The USB flashdrives can include input/output components, such as a wirelesstransmitter or USB connector that can be inserted into a USB port ofanother computing device.

The system 900 includes a processor 910, a memory 920, a storage device930, and an input/output device 940. Each of the components 910, 920,930, and 940 are interconnected using a system bus 950. The processor910 is capable of processing instructions for execution within thesystem 900. The processor can be designed using any of a number ofarchitectures. For example, the processor 910 can be a CISC (ComplexInstruction Set Computers) processor, a RISC (Reduced Instruction SetComputer) processor, or a MISC (Minimal Instruction Set Computer)processor.

In one implementation, the processor 910 is a single-threaded processor.In another implementation, the processor 910 is a multi-threadedprocessor. The processor 910 is capable of processing instructionsstored in the memory 920 or on the storage device 930 to displaygraphical information for a user interface on the input/output device940.

The memory 920 stores information within the system 900. In oneimplementation, the memory 920 is a computer-readable medium. In oneimplementation, the memory 920 is a volatile memory unit. In anotherimplementation, the memory 920 is a non-volatile memory unit.

The storage device 930 is capable of providing mass storage for thesystem 900. In one implementation, the storage device 930 is acomputer-readable medium. In various different implementations, thestorage device 930 can be a floppy disk device, a hard disk device, anoptical disk device, or a tape device.

The input/output device 940 provides input/output operations for thesystem 900. In one implementation, the input/output device 940 includesa keyboard and/or pointing device. In another implementation, theinput/output device 940 includes a display unit for displaying graphicaluser interfaces.

The features described can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. The apparatus can be implemented in a computerprogram product tangibly embodied in an information carrier, e.g., in amachine-readable storage device for execution by a programmableprocessor; and method steps can be performed by a programmable processorexecuting a program of instructions to perform functions of thedescribed implementations by operating on input data and generatingoutput. The described features can be implemented advantageously in oneor more computer programs that are executable on a programmable systemincluding at least one programmable processor coupled to receive dataand instructions from, and to transmit data and instructions to, a datastorage system, at least one input device, and at least one outputdevice. A computer program is a set of instructions that can be used,directly or indirectly, in a computer to perform a particular activityto generate a particular result. A computer program can be written inany form of programming language, including compiled or interpretedlanguages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment.

Suitable processors for the execution of a program of instructionsinclude, by way of example, both general and special purposemicroprocessors, and the sole processor or one of multiple processors ofany kind of computer. Generally, a processor can receive instructionsand data from a read-only memory or a random access memory or both. Theessential elements of a computer are a processor for executinginstructions and one or more memories for storing instructions and data.Generally, a computer can also include, or be operatively coupled tocommunicate with, one or more mass storage devices for storing datafiles; such devices include magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,ASICs (application-specific integrated circuits).

To provide for interaction with a user, the features can be implementedon a computer having an LCD (liquid crystal display) or LED display fordisplaying information to the user and a keyboard and a pointing devicesuch as a mouse or a trackball by which the user can provide input tothe computer.

The features can be implemented in a computer system that includes aback-end component, such as a data server, or that includes a middlewarecomponent, such as an application server or an Internet server, or thatincludes a front-end component, such as a client computer having agraphical user interface or an Internet browser, or any combination ofthem. The components of the system can be connected by any form ormedium of digital data communication such as a communication network.Examples of communication networks include a local area network (“LAN”),a wide area network (“WAN”), peer-to-peer networks (having ad-hoc orstatic members), grid computing infrastructures, and the Internet.

The computer system can include clients and servers. A client and serverare generally remote from each other and typically interact through anetwork, such as the described one. The relationship of client andserver arises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

Many other implementations other than those described can be employed,and can be encompassed by the following claims.

What is claimed is:
 1. A system comprising: one or more electronic portsfor receiving signals from sensors for obtaining a time domainelectrocardiogram (ECG) of a patient; and a patient treatment modulecomprising an ECG analyzer and a non-transitory computer-readablestorage medium encoded with a computer program comprising instructionsthat, when executed, cause one or more processors to perform operationscomprising: performing at least one transformation of at least a portionof a time domain ECG signal from the patient into frequency domain data,determining a first frequency-based value over a first evaluation periodbased on the at least one transformation, determining a secondfrequency-based value representing a trend over a second evaluationperiod based on the at least one transformation, determining aprobability of therapeutic success based at least in part on the firstfrequency-based value and the second frequency-based value, andproviding an indication of the probability of therapeutic success. 2.The system of claim 1, wherein the first frequency-based value comprisesan amplitude spectral area (AMSA) value and the second frequency-basedvalue comprises an AMSA trend.
 3. The system of claim 2, the operationscomprising: applying a first threshold to the first frequency-basedvalue; determining that the first frequency-based value is below thefirst threshold; and in response, determining the probability oftherapeutic success at least in part based on the second frequency-basedvalue.
 4. The system of claim 3, wherein the first predeterminedthreshold is 12 mVHz.
 5. The system of claim 3, wherein determining theprobability of therapeutic success comprises: comparing the probabilityof therapeutic success to a second threshold; determining that theprobability of therapeutic success exceeds the second threshold; and inresponse, indicating the probability of therapeutic success.
 6. Thesystem of claim 2, wherein the change of the AMSA value is determined asa difference between two AMSA values corresponding to two time pointswithin the first evaluation period.
 7. The system of claim 6, whereineach unit of the difference corresponds to a predetermined increase ofdefibrillation shock success.
 8. The system of claim 6, wherein an endof the first evaluation period and a beginning of the second evaluationperiod are defined by a preset time interval.
 9. The system of claim 8,wherein the preset time interval comprises approximately 2 minutes. 10.The system of claim 6, wherein at least one of the two AMSA valuescomprises at least one of a mean AMSA value, a median AMSA value, acenter AMSA value, and a peak AMSA value determined around a first timepoint and during the first evaluation period.
 11. The system of claim 6,wherein determining the change of the AMSA value comprises determining athird AMSA value corresponding to a second time period that issubsequent to the first evaluation period.
 12. The system of claim 11,the operations comprising determining whether the metabolic state of themyocardium of the patient is continuously improving.
 13. The system ofclaim 1, wherein the treatment comprises delivering a defibrillatingshock.
 14. The system of claim 1, wherein the treatment comprises atleast one of introduction of a thrombolytic agent, introduction of ametabolite, introduction of a metabolic enhancing agent, and applicationof electromagnetic energy to stimulate cardiac tissue at energy levelsbelow those sufficient for defibrillation.
 15. The system of claim 1,wherein indicating the administration of the treatment to the patientcomprises displaying a treatment recommendation on a display of thepatient treatment module.
 16. The system of claim 2, wherein the AMSAtrend comprises a rate of change of the AMSA value over time.
 17. Thesystem of claim 1, wherein determining a probability of therapeuticsuccess is based on a regression analysis.
 18. The system of claim 17,wherein the regression analysis comprises a statistical model thatinputs the first frequency-based value and the second frequency-basedvalue and outputs the probability of therapeutic success.
 19. The systemof claim 18, wherein the statistical model inputs a first AMSA value anda second trend in AMSA values and outputs a probability of therapeuticsuccess.
 20. The system of claim 1, wherein providing an indication ofthe probability of therapeutic success comprises sending a signal todisplay the indication of the probability of therapeutic success to auser.